Central Heating/HW System problem

26 Dec 2007
Reaction score
United Kingdom
Please could someone help me understand what the following fault is with my system.

System details:
Boiler is a Baxi Burmuda 552 (old but works fine and regularly serviced)
Programmer is a Honeywell ST699
HW Tank stat is Honeywell L641A1039
Room Stat is a Honeywell, not sure of model.
3-Way motorised valve
Wilo Gold 50 pump

The progrmmer settings were: HW set to constant, CH set to Off.

During the night the rads where hot and the HW heating up, even thought the CH was set to Off. The hot water out of the taps is very hot. I have turned the room stat to zero and the heating stills runs with the HW set to constant, but the CH set to Off.
When I turn off the HW and turn on the CH at the programmer, I can control the CH on the room stat and the HW does not heat up.
As far as I can tell, the 3-way motorised valve is working OK.

I am thinking it is a programmer fault, does anyone have any ideas?

Thanks for taking the time to respond.
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i dont think your 3port motorised valve is quite right, would appear that it is not shutting off completely on the c/htg port, usually caused by a dirty system.

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