I have a new four bed holiday house with UFH on both floors managed through two IVAR blender manifolds controlled by two Heatmiser UH3 Wiring Centres. On the supply side I have a Akvaterm Solar 2000 Thermal Store which is only heated by an oil boiler with electric immersion coils as back up at the moment. It has been set up so I have options next year for solar / heat pumps etc. There is a Main Circulation Pump to both move water from the Thermal Store to the boiler but also to take water to the manifolds. It's one loop.

An ESi Electronic Dual Cylinder Thermostat is attached to the Store but has been added after the original installation and not commissioned properly.

The Store Thermostat is wired as follows. Perm L&N. The Switch Live "Boiler Out" from the Wiring Centre is going into the HW-On Com terminal in the thermostat. A single wire goes from HWS N/O in the thermostat to a fuse input terminal through to activate theCirculation Pump. The Boiler Switch Live is inserted in the same input terminal and is made Live as the power passes through to the Main Circulation Pump. It works for maintaining the heat store temp for DHW.

However on the heating demand side, when the Wiring Centres activate, the blender pumps start as required but the Main Circulation Pump does not activate. No hot water is round the loop to the manifold from the Store. Moving the Wiring Centre Switch Live to the Main Circulation Pump Fuse input makes this work.

What is missing is the ability to activate the Main Pump from either the Store Thermostat and / or the Wiring Centre.

My thinking has been as follows ....

Bridge the Perm Live and HW-On COM terminals within the Store Thermostat. Take Boiler Switch Live direct from Store Thermostat HWS NO. Also take a Switch Live from same HWS NO terminal to Fuse input terminal leading to the Main Circulation Pump. Wiring Centre Switch Live to same Fuse Input for Main Circulation Pump.

Questions.
I think I will have a backfeed problem because SL for Wiring Centre and Store Thermostat are connected at the Pump Fuse input ?

How can I activate the Circulation Pump from either or both of the Switch Lives without backfeed ?

I want to avoid the boiler turned on every time the Wiring Centre calls. I want the boiler to be controlled solely by the Store Thermostat. My concern is SL from Wiring Centre backfeed to Store Thermostat and activates Boiler Switch Live at HWS NO Terminal which they would share.

I have run out of road on thinking this through and would welcome some advice. Are relays the answer ?

Thank you for taking the time to read my ramblings ...

+1

The two halves of our system work totally independently. They only share the FSU (switch and fuse).

Primary - The stat on the store controls the boiler and the pump that circulates water from the boiler to the store.

Secondary - The room stats go into 2 wiring centres. The two "BE" signals are logically OR'd together to control the pump that circulates water between store and manifolds.

There are no connection between the two sides. If the rooms call for heat the store delivers it without firing the boiler. Eventually the store gets cold and the boiler fires with one long burn to reheat it.

Thx for reply. Sounds,like you have two pumps and two "loops". I think I have one circulation loop from store past manifolds through boiler and back to store with one pump. I think I can wire per my original note to achieve the cycle you outline. Wiring centre activates pump and thermostat turns boiler on when temp drops in tank. However, I need to ensure Pump is always on when Boiler is on. Also, because the store also heats the DHW, I also need the pump and boiler to activate from the thermostat when the Wiring Centre is not calling for heat.

Posted By: Caterham07If I assume the pumped outflow is to the Boiler,

You can't assume!! you need to find out.
One pump can create flows and back flows on unrelated but connected loops.
Lots of boilers have circulation pumps incorporated within them, check your boiler for this.
IMO you can not solve this problem by fiddling with the control circuitry.

The way thermal stores work is that the heat source (boiler, solar etc.) heats the TS and the TS supplies the heat load (DHW or/and CH) The two circuits, supply and load, should be independent of each other.

So you should have a pumped circuit from boiler to TS (gravity with a (modern?) oil boiler probably won't be an option) and a pumped circuit from the TS to the load. Sometimes there is more than one pump on the load side depending upon the requirements and sometimes the additional pump(s) are replaced by motorised valves.

Each pumped circuit will need a non-return valve (usually located at the pump) to prevent back flows and interference from other pumped circuits. I suspect that you may be short of a couple of strategicly placed non-return valves!

But you will need non-return valves in both the boiler and heating loops otherwise back flows will cause all sorts of issues. I would be surprised if the system was installed without pumps on both boiler and load loops but I could imagine non-return valves being omitted.

Several things as I have a similar setup.

Firstly the water in the tank is both heated by the boiler and used for the UFH. If you have a system boiler, it has a builtin pump else you need a separate pump. the control of the temperature of the tank should be independent of the heating or DHW so the tank thermostat just drives the boiler and the associated pump.

Secondly, these tanks should have a blending valve on the UFH output side so it pulls the heat from the bottom first then progressively higher up. If you do not have this valve you need it to maximise the draw from the tank.

Finally you should have a dump valve that makes sure the flow to the boiler is always about 40Deg.

If you lok at this diagram you will see both valves. http://www.akvaterm.fi/eng/Accumulators/AKVA_SOLAR.41.html

So yes you need 2 pumps, one for UFH and one for Boiler. Tank thermostat controls the boiler, room stat controls the UFH pump.