worcester boscch 240 combi prob

[newbie1]

ok guys strange one
worcester 240 combi works fine on downstairs tap
if she runs a bath and turns the hot off it knocks out the pilot light
have changed thermocouple anyway as it was hard to light
only does it when she is running a bath???
answers on a postcard please

 

[GavinSmith77]

had this the other day i think its the hot water heat exchanger thats scaled up

 

[Billy Bob Bob]

or a knackerd pump or high limit stat

 

[LIFES A GAS]

Is it just about the time you are running the boiler? if you run the kitchen tap for say 5 mins does it still lock out? I had this problem with a Vaillant,customer said only locked out when running bath tap, turned out builders had erected scaffolding outside and the planks were inline with the flue outlet and deflected flue gasses back into air intake but took a few mins before the boiler locked out so running kitchen & basin tap did not cause lockout.
Martin.

 

[newbie1]

there have been no changes that could have effected boiler etc its my guess heat exchanger is blocked so oheat stat is kicking in due to struggle to heat the water

 

[LIFES A GAS]

Don’t think so!, the overheat stat has to be manually reset and you did dent say you had to do that, if your pilot is difficult to relight as you said, have you cleaned & adjusted it? could be it's being pulled away from the thermocouple when the main burner is at full rate, Does the boiler lock out on heating?
Martin.

 

[newbie1]

thermocouple has been replaced def oheat stat kicking in
i stood there while she ran the bath (very slow flow rate)and sure enough before bath is full it knocks the gas valve off incl pilot.no heating is fine so it is related to the dhw when boiler is working the hardest

 

[LIFES A GAS]

OH, is the tap on the bath opening fully or is there an isolation valve inline not fully open? strange it only locks out on the bath tap, would have thorght if it were water to water heat exchanger restricted by scale/sediment it would lock out on all taps.
Martin

 

[rob jefkins]

Probably crap in the heat exchanger mate. Had the same problem with one last week. Took out the heat exchanger, flushed it through with acid. No probs since. Might be some crap in the pipework as well though

 

[newbie1]

my thoughts exactly shes going to wait and have new boiler in a couple of months