Discuss Thermal Store problems in the Central Heating Systems area at ElectriciansForums.net

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First, I agree with PEG (#20) about employing an electrician to inspect and test in order to diagnose the electrical fault.

I am interested in helping you with this plumbing aspect of your problem:
' All working well for the past year, apart from rads getting hot then cool (as the water gets pushed round the system) so instead of standing with my hand on the rad flow pipe to turn the heating off in order for the store to heat up again, I wanted a pipe stat to turn the pump on at temp (55 deg?)'

I wanted to see an 'as installed plumbing diagram' to see where you had located the pipe stat - I assume you have put it into the radiator flow out pipe from the thermostore. I think this will be problematic because you will indeed have flow when the flow is above the preset temperature but when the temperature drops and the stat turns off, so does the flow; consequentially the water in the pipe will cool down - because there is no flow - and there can never be any further flow because the pump is not running because the stat is off because the water is too cold.

I think the pipe stat should be placed in the out flow pipe between the back boiler and the heatsink radiator after the normally open valve which feeds it. This way the pipe stat will detect when the water in the thermostore is at a high enough temperature to allow flow to begin through the other radiators. You would use the Normally Open contacts of the pipe stat in series with the pump line supply. By some trial and error you can set a suitable switching temperature. More simply this arrangements makes the household radiators warm up in tandem with the heat sink radiator and stops flow when the hot water from the back boiler is diverted to heat up the thermostore. It also stops the pump running when the back boiler is not lit.
 
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Thank you, Marconi, for your detailed reply. Very much appreciated. Wouldn't I still have the same problem though, regarding the cold CH water being pumped around and then waiting for the store to heat up again? With the pipe stat on the outflow from the store, I could set the temp at a min of 50-55 deg otherwise I am waiting for the cylinder stat to open the heatsink at around 85 deg?
 
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If you have someone coming out,then hopefully you can get sorted and clean:) ....but if your system looks identical to that generic picture...i'll dress as Gladis Emmanuel and bed-bath you myself ;)

At this moment in time... I'll take it! :joycat:
 
Assumptions:

1. Solid fuel back boiler lit.
2. Timed on period for CH.
3. Room stat below fixed temp and hence on.

Now, with the thermostore at or above its tank stat temperature, the tank stat normally closed contacts are open which removes power from the heat sink radiator's normally open motorised valve -this valve opens allowing hot water under gravity to flow.The normally open contacts of this valve are open which removes power from the normally closed motorised tank valve between the back boiler and thermostore - hot water from the back boiler no longer flows through the thermostore heat exchanger. A pipe stat on the flow to the heat sink radiator will detect hot water and when above preset temp close the normally ope contacts supplying power to the pump. The pump circulates water through the other radiators, this water being heated by an exchanger in the thermostore - the thermostore water cools while heat is taken from it. When the thermostore tank stat drops below preset, its normally closed contact close which energises the heat sink radiator valve to close which in turn energises the normally closed rank valve to open. The back boiler now heats the thermostore again and flow through the heatsink radiator ceases; the water in the pipe cools and is sensed by the pipe state which eventually drops below preset enough to turn off the pump. There is thus a cycling between two states which depends on the rate at which heat is supplied to the thermostore by the back boiler circuit, the rate at which its is removed by the CH circuit, the upper temperature when the tank stat normally closed contacts open and the lower temperature when the same contacts close (hysteresis effect eg if you set 70C they might open at 75C and close at 60C which is important to prevent a rapid cycling rate which would be the case for say 71C and 69C).

What I think is a problem/feature you will have to contend with/accept is that the back boiler is relatively low powered compared to a gas boiler and relies on gravity flow. These factors mean it will take 'longer' to heat the thermostore by a back boiler than a powerful gas boiler. Ultimately energy is conserved and over time you cannot get out more heat energy than you put in. As controlled the system prioritises keeping the thermostore at its set point temperature, so if you drain the tank say for several large baths of hot water the CH and heat sink radiator will be off for a while as the back boiler heats the thermostore up.

Long winded - sorry. You get the gist. Others might have better ideas to contribute.

PS: My plumbers friends don't understand why the CH is fed by a heat exchanger in the thermostore rather than directly from the back boiler via a tank/CH diverter valve. But that is what the manufacturer's thermostore diagram shows, I guess to enable several sources of heat energy to be stored in one tank through a number of heat exchangers eg: gas boiler, solid fuel back boiler, solar panels, heat pump...
 
Just a little point,here,if a heat-sink radiator,is genuinely that,it will definitely not have a motorised valve,negating it's operation.
 

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