Vaillant 242 combi

[hendert]

My old 242 starts ok on water all the time and on c/h when cold however once c/h has been on for a while rads seems to get hotter than normal it cuts out and then struggles to ignite again, if I hadn't spotted it I think it would have self destructed, I think it might be the c/h return safety switch which is not resetting correctly the small one the size of and "old threepenny bit" this played up once before and I think it is series with the gas valve.
Any help or thoughts would be appreciated.

 

[Agile]

An overheat stat is on the flow pipe not the return.

There could be several causes of overheating but the first to consider is the temperature sensor.

It could also be a seriously misadjusted gas valve and those kind of faults would normally be discovered by an observant gas engineer on a service. ( Whats that? ).

Tony

 

[kevplumb]

There could be several causes of overheating but the first to consider is the temperature sensor.

not being sarky tony but ive never known a vaillant ntc fail the herbs are bomb proof usual fault is a bad connection on the spade

BTW happy new year

 

[Agile]

I agree that they rarely fail on this model but when I suggest a "temperature sensor" I mean the sensor, its connection and its lead.

Too many words to repeat so often!

Happy new year!

Tony

 

[hendert]

Replacing the sensor seems to have sorted it, thanks gents for taking the time and trouble to reply.

 

[Agile]

Now just for Kev's information, do you think it was the sensor itself, the connection to it or the lead?

( Sorry, or the other alternative, "you dont know"? )

Now for engineers, I was removing a failed 1999 vaillant condensing boiler ( an 836 ? ) last week and it had TWO similar NTCs just about 10 mm apart on the flow pipe. Does anyone know why?

Tony