Any ideas? Combi tries to supply DHW after a CW demand

[blondini]

Any other suggestions or thoughts would be most welcome as this is driving both myself and the original installer to distraction.

Many thanks

I'm not a qualified plumber but you are welcome to my considered thoughts.

I would investigate the possibility that air is trapped within the DHW circuit in the boiler itself. I don't know what mechanism is supposed to vent air in this location, but I would look into that, and also the HE which may be flawed and have trapped air.

With air trapped as described, a closed valve on the HW outlet would make no difference, and a check valve on the cold water inlet would make little difference as the pressure blip from closing a cold tap would still pass the valve and briefly spin the aquasensor, (which sounds like it is working correctly).

 

[HARALIAN]

Do you have a tmv on the system or mixer taps? ( as DM asked) Hot n cold aint crossed ( may sound too simple eh?) Isolate certain taps etc ( too logical)and then test for HW firing up again....How about popping a tap on the hot water outlet and isolating the ret of the house and see what the boiler does then!? Is it the boiler or the pipework??? Sounds pipeworkish to moi in my humble opinion! We had the same thing a while ago on a Worcester....... We ended up re-piping the whole house as we couldn't get in everywhere to see the existing pipes.

 

[HARALIAN]

Whoops.... just read back and youve tried all of this ... soz.... try getting Vaianl Valiant vatalli
those boiler bods to sort it out!!!!