if he saying h/w is on all the time (boiler firing) - could be a stuck DHW flow switch....
but I agree diverter valve passing is allowing rads to heat up in pre-heat mode
thanks dave18 for your help.
if the secondary heat ex was blocked - on the ch side (not cold going in - hot out) then i've heard the water will run hot then cold hot then cold like that and could even overheat lockout.
if the water slow from a combi was poor it could also be a blocked/part...
I know that, but also it could be down to a sludged up system, as newer boilers have smaller heat ex's and they can get blocked.
About the pump: do you mean the pump failing/slowing...
What would you say the best/easiest way is to fault find a sludged up heat exchanger that could be causing no/poor circulation and boiler overheat/lockout?
The poster needs an boiler breakdown engineer to check everything in the boiler and to find/replace the part ideally.
One last point dave18: what would you say the best/easiest way is to fault find a sludged up heat exchanger that could be causing no/poor circulation and boiler overheat/lockout?
dave18 - of course it would, soryr for that one of those lazy days!! :lol:
I agree with you about the CH flow seitch being stcuk in the ON position, and if the pump was faulty the no circulation would cause the boiler to overheat (on CH or DHW demand) - so 2 faults in 1 there. (as if...