DIY Doctor

Central Heating Only Normal From Cold

Postby keratos » Fri Dec 06, 2019 1:52 am

views please...

so...
My system is modern unvented, indirect HW tank, S plan . House is 10yr old, a 3 storey townhouse with 10 rads. Geo Cosy system (fitted by Shell Energy) controls the CH using the Cosy Hub to detect room temperature, the desired temp set using the Cosy app. Rads are balanced (top floor 1/4 turn out on all lock shields) , middle floor maybe 1/3 turn out, ground floor are about 1/2 turn out. all warm up about same time and get hot . All have TRVs.

right....
From cold, the house warms up from 15 to (desired) 19.5C in about an hour. All rooms are all good. CH demand correctly switches off at 19.5C. Residual radiated heat takes the room temp to 20C. But, with rads now cooling down, the temperature starts to drop . At 19C, the system correctly demands CH again but the boiler does not fire. The temp continues to drop and not until about 45mins to an hour later, does the boiler fire up. All the time, the CH demand is on, the electrical CH zone valve is correctly open and HW is off. The secondary pump is running but boiler is off ...although the pump does eventually turn off too after about 20mins.

Wait about an hr, and it all starts working again... but the cycle is repeated.

???
keratos
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