C Plan DHW relation to CH, some insite please.

27 Jan 2008
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Llanfair Caereinion, Nr Welshpool
United Kingdom
There may be nothing wrong. The DHW is thermo syphon and CH pumped, there is no motorised valves on the DHW, but there are on the CH as two zones (Main house and Flat) and we were getting reverse flow when only one of the two pumps used, so motorised valves added to stop reverse flow and it has worked.

In summer the DHW runs 4 times a week for ½ hour at a time, well really 20 minutes as boiler switches off after 20 minutes even if Nest Gen 3 is calling for heat for ½ hour every other day.

In winter DHW turned off, it heats with CH anyway.

But noted boiler only running for 20 minutes before it starts cycling on/off, at first thought on radiator at fault, batteries gone flat, and the default with flat batteries is open with the electronic TRV heads I am using, so batteries replaced and also lock shield valve turned down a bit.

However the boiler is still cycling before any radiator is really hot, but the pump (fitted on the return) is hot, so big question is why?

What I am wondering should I throttle back the DHW in the winter?

When we moved in it was clear the previous owners did not use the CH but lit wood burning fire, to turn CH on had to go out side down a set of steps and plug in the pump. Seems when garage made into flat the heating was set up to heat flat under house, but the house heating completely messed up.

This is only our second winter here, and until now had either combi boiler or separate boilers for DHW and CH. Also was using gas, but here no gas so using oil.

I know my parents had C Plan, but CH only used to remove chill before lighting fires, so I don't know what to expect. The boiler man said to fit a motorised valve on DHW could cause over stressing of boiler as no cool down sequence. Oil boilers not cheap, so don't want to stress boiler.

So some insight as to what I should expect. At moment 10°C outside at 2:30 am so bedroom lovely or maybe a little too warm at 21.3°C the extra loft insulation has warmed up this bedroom so some adjustments required. But when outside temperature drops the system does not seem to cope, which is mainly due to boiler cycling before all radiators warm, rather than boiler too small.
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