Green Building Forum - MVHR overheating warning Tue, 19 Dec 2023 04:01:16 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301138#Comment_301138 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301138#Comment_301138 Sat, 08 Apr 2023 11:53:01 +0100 Rex
I have a Flexit (Helios?) L4X HVMR unit which I installed when I built my house, around 12 years ago. I change the filters regularly; it runs around 8 hours per day over three different time periods. The last period is the late evening and I press the central button on the control panel for a 30 min high speed boost to remove moist air from the bathroom.

It is connected to the UFH pipework so when the UFH is on, there is a bit of pre-heating of the incoming air.

Recently, too frequently, I seen the panel (image below) with the red warning LED (top) illuminated. According to the instructions, this is an overheating thermostat warning light when the unit starts. The solution is in the loft, (very inconvenient following a both!) press the 'Reset' button. Usually, I also unplug before resetting.

Back at the control panel, sometimes pressing the two temp buttons (left and right buttons) simultaneously is necessary, but the unit then starts and works fine.

There are only two thermostats that I am aware of; one on the supply side, after the unit to measure the air temp and one within the heat exchanger. I have cleaned both.

My problem is that I have no idea what overheating thermostat actually means, where to find it and how to cure the issue.

Grateful for some advice.

Many thanks and toodle pip

The photo show the panel in warning' mode. The left/right -/+ set the temp, which with both red lights on, is 20C as need to reset via this panel. The C light is sometime on and sometime not; don't really know what it is telling me!]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301141#Comment_301141 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301141#Comment_301141 Sat, 08 Apr 2023 13:35:25 +0100 djh
edit: presumably your UFH connection is actually a post heater? In which case is the thermostat before/after/within it? Is the UFH on? i.e. could the problem be hot water flowing around when there's no airflow.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301143#Comment_301143 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301143#Comment_301143 Sat, 08 Apr 2023 14:35:35 +0100 Rex
Yes, the heater 'battery' is on the exit side of the unit and the thermostat is about one foot further along the supply duct. The UFH is currently on, but it is weather compensated so at the moment, does not actually fire up. And if it is running, the max flow temp is around 38C; never been a problem in the past so don't know why it would be now.

I have sent an e-mail to the Swedish manufacturer but after ten days and no response, wonder if I am being ignored.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301151#Comment_301151 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301151#Comment_301151 Sat, 08 Apr 2023 23:30:32 +0100 Mike1 Posted By: RexI have sent an e-mail to the Swedish manufacturerHave you got the correct manufacturer? Looks like they could be Finnish?
https://www.onninen.fi/en/onnline-control-panel-energy/p/AHN331]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301152#Comment_301152 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301152#Comment_301152 Sun, 09 Apr 2023 11:22:12 +0100 Rex
https://www.flexit.no/en/products/air_handling_units_300-700_m-h/expired_models_automatic_300-700/control_panel_ci50/

Yesterday afternoon, not having reset anything, the unit came on and was running as it should. It them goes off for a few hours, coming on again at 22:00. At 22:00, it should overload mode again.

This morning, again, overload mode; went into the loft and reset the unit, then the -/+ temp control to reset the panel (or whatever doing that resets) and the unit is working as it should.

The external and internal temps are such that the UFH has not come on.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301153#Comment_301153 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301153#Comment_301153 Sun, 09 Apr 2023 11:39:13 +0100 djh Posted By: Mike1
Posted By: RexI have sent an e-mail to the Swedish manufacturer
Have you got the correct manufacturer? Looks like they could be Finnish?
https://www.onninen.fi/en/onnline-control-panel-energy/p/AHN331Certainly that looks like the control panel. The MVHR manufacturer is apparently Norwegian, with a Swedish factory, according to https://www.flexit.no/en/about-flexit/about-us/ and an American domain for email export@flexit.com !]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301157#Comment_301157 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301157#Comment_301157 Sun, 09 Apr 2023 18:57:05 +0100 Rex MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301182#Comment_301182 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301182#Comment_301182 Wed, 12 Apr 2023 14:57:51 +0100 Rex
Did a Dr. Google search to see how to test these things, ans appears that if thee is continuity, all should be OK.

Thermostat in the photo is the rest button (which probably only has around 0.5mm of movement IF in the raised position) and I get a continuity sign from it.

The other (to the left of the photo) does not have the button, and there is no continuity. Presumably, it is therefore not working? If that is the case, why when the MHVR fires up with the warning light, and I go to the loft to reset the button, the unit then runs fine if this stat is not working?

Is it a wise assumption that this stat is faulty, always open and should be replaced?]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301184#Comment_301184 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301184#Comment_301184 Thu, 13 Apr 2023 08:06:46 +0100 GreenPaddy
- it appears the sensor isn't "just" a temperature probe (like a PT100 or some sort of resistance probe). It is a fail-open type of stat, which requires manual intervention to re-set. A simple temp probe would be tested by checking the resistance over its range (ice water, boiling water etc) and comparing with the manuf's table of resistance versus temp.
- I'd guess that there are two sensors, one that measures temperature, and the second (with the reset) which is the fail safe control trip. As above, two different pieces of kit.
- assuming there is no excess heat input to cause a "true" overheat scenario, the problem is that the temp stat "trips" at the wrong temperature, ie. it's faulty.
- I imagine the stat will be maybe £20. I'd order a new one and just replace it. That's the only way you'll know if it is the stat, or some other issue. If the manuf wants a silly price for the stat, you can likely study the details of the stat, and buy an identical off 'tinternet. The MVHR manuf will have bought the stat from a stat manuf, just as you can.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301185#Comment_301185 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301185#Comment_301185 Thu, 13 Apr 2023 09:12:43 +0100 Rex
Have made a bit of progress in my understanding. Not sure I understand why the overheating / reset stat is on the incoming air flow, but having removed it, shaken it a bit and wiped the base with a damp rag, for the past 24 hrs, everything is working as it should.

Regarding the other, non-resetable stat, I now believe that to prevent the unit from freezing so obviously only works if the incoming temp is very cold, and as a result, activates the electrical pre-heater. Obviously, in normal conditions, it would be open, which it is.

Replacement stats are available from Sweden/Norway, but will continue to monitor before replacing.

Thanks everyone for your thoughts.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301186#Comment_301186 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301186#Comment_301186 Thu, 13 Apr 2023 10:09:53 +0100 WillInAberdeen
If so, the stat has an important safety function and you should replace it. It is there to stop the electrical heater running if the airflow became insufficient to carry away the heat, for any reason (blockage, fan failed) and so causing overheating/damage/fire. It is purposely made difficult to reset so that people will investigate the safety fault rather than just resetting the sensor.

If replacing the stat doesn't stop it tripping, then there is a safety problem with the preheater.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301187#Comment_301187 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301187#Comment_301187 Thu, 13 Apr 2023 11:41:25 +0100 Peter_in_Hungary Posted By: RexReplacement stats are available from Sweden/Norway, but will continue to monitor before replacing.
Posted By: GreenPaddyThe MVHR manuf will have bought the stat from a stat manuf, just as you can.

Components often have an identification number printed on them and a google search on that number can give a few options for sourcing the component - which allows you to order at the best price / convenience.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301188#Comment_301188 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301188#Comment_301188 Thu, 13 Apr 2023 12:58:31 +0100 Rex
Will have another look, although that does entail removing it again.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301189#Comment_301189 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301189#Comment_301189 Fri, 14 Apr 2023 11:12:51 +0100 Rex
However, in the past 24 hrs, there have been four on/off cycles and no overheating warnings. Have not done anything specific to fix the stat so time will tell.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301190#Comment_301190 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301190#Comment_301190 Fri, 14 Apr 2023 11:56:20 +0100 WillInAberdeen
You can use this info: a) to check if the stat is tripping at a sensible temperature or if the fault lies elsewhere, and b) to search for an equivalent stat.

(And - obviously - stop before anything melts!)]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301191#Comment_301191 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301191#Comment_301191 Sat, 15 Apr 2023 13:19:25 +0100 Mike1 MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301195#Comment_301195 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301195#Comment_301195 Sat, 15 Apr 2023 19:40:04 +0100 Peter_in_Hungary MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301722#Comment_301722 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301722#Comment_301722 Sat, 27 May 2023 10:13:47 +0100 Rex
Some progress but.... Email to Sweden for a replacement stat and informed they will not ship the part to the UK.

It is a 16/250AV Normally Closed 80C, manual rest stat but the base has a smooth shape that allows it to fit flush into the incoming air flow.

However, I have found many that will fit but they all have a base which will not fit flush in the hole, although the stat will fit in my MCHR unit as the bracket dimensions are the same.

The second photo is a typical example of what I have found on the net.

First question; why does all my Google searching only find stats that look like that second photo? Cannot find anything that resembles my current stat base. As the second will fit but the face will not protrude into the air flow, am I likely to encounter any difficulties?

Secondly, it appears that the most common stat is 10/250AC but my current is 16/250AC. What happens if I fit a 10/250AC?

Third photo is the current stat. Where can I find a stat like the existing one?

Thanks and toodle pip]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301723#Comment_301723 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301723#Comment_301723 Sat, 27 May 2023 11:27:17 +0100 Mike1 Posted By: RexCannot find anything that resembles my current stat base. As the second will fit but the face will not protrude into the air flow, am I likely to encounter any difficulties?I can't imagine that a 2mm projection would make a great deal of difference. However I can see a couple of stats that do project - the Fagor Brandt 283311AAC and 95X0080 (may be the same product) - which I assume are normally closed as they're also safety thermostats, but not sure what their dimensions are. For example https://spares2repair.co.uk/fixed-value-thermostat-limiter-safety-80o-fagor-brandt (available for ¼ of that price in Europe). Zooming in that looks like 16A 250V AC too, though that may be a 4 in brackets on the Ampage?

Posted By: Rexthe most common stat is 10/250AC but my current is 16/250AC.
That will be 16A 25V AC current, the maximum it can safely handle

Posted By: RexWhat happens if I fit a 10/250AC?
If your HVMR unit is running at 230V and protected by a breaker of 10A maximum (I'd guess it may be 2A?), it should be fine.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301760#Comment_301760 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301760#Comment_301760 Fri, 02 Jun 2023 11:03:25 +0100 Rex
For the past week, the MVHR unit has started just fine, including in the morning when the outside temp is cooler. Until this morning!!!! when the alarm red light was on. Resetting on the control panel does nothing, until I have rest on the manual rest stat.

However, before resetting the stat, although I disconnected the two terminals (have to to that to get access to the connectors) and took a continuity reading. It should be closed and it was. I then applied a bit of heat to its base with a hair dryer and sure enough, it opened. So perhaps it is working?

But this is what I don't understand. On the air inlet, there is an electrical pre-heater, then the two stats (one 16/250V, N/C, manual reset, apparently set to 80C. The other with no rest and I am not sure what it does) before the inlet filter. When the unit goes into alarm mode, disconnecting the manual reset stat for a few seconds / wiggling the reset button, and resetting with the buttons on the control panel, and all is fine.

Given that the 80C stat is presumably to prevent 'hot' intake air getting too hot (but 80C is hotter than the average sauna!) and the stat is normally closed and seems to be working, why would it be causing an 'alarm' when a/ the pre-heat is not working and b/ there is no way the incoming outside air is anything other than cool?

What would happen if I disconnect both pre-heat element and the incoming N/C (possibly faulty?) stat?

I'm not sure if the pre-heater has ever worked as here in leafy Surrey, we do not get below freezing temps very often.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301762#Comment_301762 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301762#Comment_301762 Fri, 02 Jun 2023 12:30:53 +0100 WillInAberdeen Posted By: WillInAberdeen While you have it out, put it in the cold kitchen oven. Turn the oven on to its lowest setting so it slowly warms up. Every minute, measure the oven temperature with a thermometer and check if the stat has tripped yet. Stop when it does, and note the final temperature

You can use this info: a) to check if the stat is tripping at a sensible temperature or **if the fault lies elsewhere**, and b) to search for an equivalent stat.

(And - obviously - stop before anything melts!)The 80⁰ safety stat is there to prevent a fire/meltdown if the fan airflow ever got blocked/stopped whilst the heater was energised. The other stat is the everyday on/off control that decides if heating is required today depending on the weather, test it in your freezer. There is no guarantee that either one still works at the original specified temperature, until you test...!

If you are considering disconnecting the safety stat , you need to be 1000% sure the heater is disconnected first, and label it all up or cut the terminals off so no future trades/owners reconnect it without the safety stat in place. The 'alarm' might go permanently on.



Even if not needed for heating the house, the preheater is possibly also intended to stop the heatexchanger condensation from freezing onto the fan on frosty mornings and unbalancing it (even in Surrey). Other models handle this problem by stopping working on frosty mornings, or by having bulletproof fans located on the warm side.

The safety stat should physically disconnect the heater (in series, breaks the circuit) and the control unit should notice that the circuit is broken and put the red light on. Could something else be breaking the circuit and causing the alarm to be logged, eg intermittent dodgy connection in wiring, or heater element burned out? Check continuity all round the circuit.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301766#Comment_301766 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301766#Comment_301766 Fri, 02 Jun 2023 15:06:28 +0100 djh Posted By: WillInAberdeenEven if not needed for heating the house, the preheater Preheaters can never heat the house, because their heat is immediately exchanged with the outgoing air! They are, as you say, to eliminate the possibility of condensation freezing within the MVHR unit, either within the heat exchanger or possibly on the fans or ducts. PH-certified MVHR units are required to use pre-heating rather than varying the ventilation rates. A post heater can be used to heat the house.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301769#Comment_301769 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301769#Comment_301769 Fri, 02 Jun 2023 16:23:27 +0100 WillInAberdeen
But I suspect that the heater is still being used for defrosting. Rex is happy to switch the unit off many hours of the day (PH notwithstanding) which would be a more energy efficient way to cope with frosty mornings.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301806#Comment_301806 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301806#Comment_301806 Sun, 04 Jun 2023 11:24:22 +0100 Rex
The alarm warning seems to be somewhat random. Sometimes it is on and the unit will not run; other times, both he alarm and element heating light are on. Most times when starting, it runs just fine.

Given that the outside temp is certainly not below freezing, why would the pre-heat element be active? Since I am not in-front of the panel when the power comes on, it could be that the pre-element heats up, and causes the stat to open, hence the alarm and non-running until reset.

In which case, what can I do to 'test' the pre-heat element? If I check it now, it will show continuity. But something could be causing it to activate even on summer mornings. Having said that, the panel displayed an alarm light last night!]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301810#Comment_301810 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301810#Comment_301810 Sun, 04 Jun 2023 12:47:49 +0100 WillInAberdeen
It is worth persisting with this, problems with the safety overheat on electric heaters need to get bottomed out, don't want a fire! If a red warning light kept coming on on a car, we wouldn't keep resetting it and driving on... (ahem).]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301818#Comment_301818 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=301818#Comment_301818 Sun, 04 Jun 2023 20:50:35 +0100 Rex
Extremely good point.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=302014#Comment_302014 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=302014#Comment_302014 Fri, 16 Jun 2023 12:51:15 +0100 Rex
I am assuming that something like this

https://sinolec.co.uk/en/manual-reset-thermostat/1211154-thermostat-80-closed.html

will be the cure? Is there any reason that I should not try this?

Thanks]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=302051#Comment_302051 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=302051#Comment_302051 Tue, 20 Jun 2023 13:31:01 +0100 CWatters MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=302063#Comment_302063 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=302063#Comment_302063 Tue, 20 Jun 2023 14:13:18 +0100 Mike1 Posted By: RexI am assuming that something like this
manual-reset-thermostat/1211154-thermostat-80-closed.html
The specification looks OK to me, and the price is very affordable.

Though, as CWatters says, it could be a loose connection.]]> MVHR overheating warning http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=304398#Comment_304398 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17808&Focus=304398#Comment_304398 Sun, 26 Nov 2023 12:11:05 +0000 Rex
However, now we are in the colder winter months, the alarm light is coming on more frequently. Seems to be that cold air on the inlet is triggering the n/c thermostat, but that really does not make sense to me.

I have visually checked for a loose connection but nothing is obvious. Is there another way to check? The inlet chamber has an electrical pre-heater that I have never used, so the stats are obviously there to prevent overheating.

I am wondering, could I take the pre-heater out of the circuit and so there cannot be an accidental future 'on' situation, and join the stat wires together to by-pass the stats?

I have ordered a couple of new (Chinese?) stats but they will require a bit of adaption to actually mount to the MVHR unit. Not a big deal.

With the recent alarm illuminated, turning the unit off, wiggling the manual reset, disconnecting and reconnecting the stat spade terminals, unit plugged in again and press the control panel reset buttons, and it usually fires up as it should.

Don't know what is next?]]>