Hi dereke,

can I just check regarding the thermal store, apologies if you're fully aufait with thermal stores. Just want to make sure advice is offered against a correctly understood problem.

210 litres sounds pretty small for a TS. Can you confirm that the cylinder does have a fresh water coil or heat exchanger, and the 210 litres is actually 'dirty' water from the boiler and radiators etc?

Is it open vented (small expansion tank somewhere above it), or a pressurised/sealed system (little blue/red metal pot that you top up the pressure occasionally from a mains connection).

If it is truly a thermal store, and not a buffer tank, or a hot water cylinder, then a couple of options might be;

- add a small destratification pump, which would push the hot water from the top of the cylinder, to the bottom, so allowing much more immersion energy into the stored water. Need to think carefully about the controls, so it doesn't run just when you're needing the hot water from the top. Would have to plan the logic to that (eg top to bottom difference in temp AND solar energy input AND maybe a time lock out (only between 10am and 2pm), etc.

- similar to above but add an inline electric heater, to heat the water as it is cycled from bottom to top (the heater of course linked to the solar diverter. Again would need some logic to make sure the flow of water matched the power input (ie. can get to the point where only say 200W is incoming, which would mean a low flow of water to allow a temperature rise. Or just treat it as a de-strat pump with a wee added bonus.

- re-think the system, what you're trying to make it do to be much more effective, and then purchase the parts to make that happen (eg larger TS, immersions in upper and lower sections, good connection positions to maximise the input and draw off, adding any other heat input source like a log boiler stove, add extra connection for say future UFH take offs, or maybe include for adding a future ASHP etc). Need to consider the entire system, so you don't miss an opportunity, as a new TS will run to £1500/£2000 plus installation. That's a big spend, and a lot of carbon just to get a bit more solar input, good as that may be.

A starter for 10

https://openenergymonitor.org/forum-archive/node/2422.html has some good discussion.

Have you considered if it might be better for the climate to export the solar PV to displace an low-efficiency fossil power station, while using a high-efficiency oil boiler to heat the hw? This is what the 'export tariff' is intended for.

Posted By: derekeit is a Gledhill THP210SOL

Hmm, seems like Gledhill have changed their range and website so there are no details of that model online. Seems a bit poor of them to take down information about previous models. I have a 250 L Gledhill Torrent OV that has two immersions (sorry, forget the model number) and it works well for two of us, with occasional visitors.

One additional thing to check first is that you are not losing heat into the central heating pipework, even when it is not switched on. Just adding a destratification pump to your existing setup seems like the simplest solution to your problem. If you do decide to replace the store at some point then getting one with another immersion at the bottom is a good idea.

The stove uses the thermosyphon effect rather than a pump.

The first thing I tried was to turn off all the rads (except the only main one without a TRV) and then try to get the heating to switch on. Only problem was that the thermostat on the stove output wasn't being tripped because there was no heat coming from the stove. I suppose I could replace that sensor with one in the store and then that plan would work. The obvious drawback being I would be pumping heat into the house just to stir up the hot water - this might be OK as an interim solution though.

I guess the next step would be to plumb in a bypass for this, I suppose that means drawing down the water from the store, soldering and recommissioning. I do a lot of things myself but I might have to get someone in for that.

The store does feed the CH as well. It did seem small to me but it was already in the house when we bought it.
Agree the ASHP is last resort, I've got some tricks up my sleeve before we have to go for that!

@djh they did send me a copy of the documentation when I emailed them and were generally very helpful but I agree they should leave the old versions online!

Posted By: derekeI have a 210L thermal store with an immersion backup and solar on the roof.
I've had a Solar Diverter installed so that we get some carbon free hot water (our main heating is oil).

This is all working great except we don't get much hot water, this seems to be because the immersion is located half way up the store so when we have a good sunny day it only heats up half way.

Is there anyway I can get the whole store heated?
Should I get another cylinder with an immersion at the bottom?

Posted By: derekeIt does have a heat exchanger for the DHW

You say the TS internal water is CH water so I presume the TS takes heat from everything and supplies both CH and DHW with the DHW heated by a heat exchanger.

It sounds like the solar is PV not ST

The general advice is to separate the CH and the DHW. Even more so with a TS that is only 210lts. I would be inclined to get a separate DHW tank prioritised over the TS by thermostats and valves (thermostats only if it is PV) or better (cheaper) to just use the solar and a backup immersion in the DHW tank because when you need the CH you won't be getting that much solar anyway. - Down side is the space needed for a DHW tank.

Based on that diagram, I assume that the oil boiler is connected to the input of the 3-port valve, so that it heats either the radiators or the thermal store. Is that correct? Also that is the only thing that heats the radiators; the thermal store and the wood stove do not heat the radiators. Is that also correct? You said that the store does heat them, so I am confused.

The drawing shows the heat exchanger for the DHW mounted horizontally and with all connections at the same level. That seems unlikely. It is normal to draw water from near the top of the tank and return it close to the bottom of the tank for this purpose. Is that not the case in your system? If it is the case then they would be good places to connect a destratification pump. Alternatives would be the unused bosses at the same height as the connections for your wood stove, but the higher you can get the input to and the lower the output from the pump the better.

dereke,

I just understood your comment about solar thermal...you don't have solar thermal panels, but you do have the solar therm coils. Your suggestion to use that as the heat input point could be a good non-invasive way to go about this.

Alternatively, you might be able to short circuit across between the outlet from the oil boiler pump (there will be a gate valve at the pump for isolation), and the feed from the oil boiler before it goes into the 3 port (again may be an isolation valve at the 3 port for servicing, but if not force it to central heating, so at least the therm store is isolated.
With a motorised valve in that short circuit, you could fire up the oil boiler pump and open the new motorised valve to give you de-strat.

The diagram shows the the oil boiler feed half way down the therm store...is it really? That means the oil boiler will never give you hot water at the top of the therm store.

Along with djh questions above, may need to clarify the drawing, or just hand sketch it. Un ugly, correct hand sketch is much better than a pretty, wrong drawing.