Central Heating

CH pump runs all the time when hot water is on, hot water cylinder thermostat not satisfied.

Anonymous user 16/03/2024 - 2.50 PM

Greetings, We have roughly 11.5 years old CH system which uses Worcester Greenstar 15ri standard boiler + hot water cylinder. Recently, the external pump would not stop running when the hot water is on (only HW), even after the boiler is has stopped running. The simplest way to describe is as: Hot water on > boiler fires and runs for around 20-30 mins > water gets hot and boiler stops > pump continues to run with very low speed and never stops. The system works fine with central heating, it's only the hot water call that causes this issue. I did some checks and it appears the cylinder thermo (Drayton HTS3), which is set to 60, never gets hot enough to turn it off. If I manually turn down cylinder thermo slightly till turns off with 'tick' sound, pump overruns 3 mins and then stops (as expected). I then gently turn up the thermo to 60 without ticking it 'on', but eventually, cylinder temp goes down, the heating starts and same issue starts again. I replaced the cylinder thermo with a brand new one, reduced the cylinder thermo to 55 and maxed boiler temperature, nothing made any difference. Should I try another cylinder thermo (i.e. honeywell) or may be the issue is with boiler? Any advise will be much appreciated. --------------------------------------------------------- For anyone experiencing similar, it turned out an issue with the drayton cylinder thermostat. Replaced with honeywell stat which is working perfectly.