Baxi duo tec combi problem

[3083sam]

I've got a baxi duotec combi and when i run the hot water, the temp guage shoots right up, then there is a clunking noise in the boiler, no error codes are coming up. The pressure guage is also shootin up and down but when the boiler cuts out the guage stabilises. Its obviously overheating.. Any ideas anyone??

 

[Whn1]

Does it shoot up straight away?

 

[3083sam]

Yes within a few seconds...

 

[Mike Jackson]

Blocked secondary heat exchanger or failed pump are my first two thoughts.

 

[Whn1]

If the plate hex was blocked wouldn't he hw come out Luke warm?

 

[quality]

sounds like you need a gas registered engineer to sort your boiler. not being cranky or sarcy but it is not what you obviousley think it is

 

[3083sam]

I am actually a gas safe registered engineer, just wasnt to sure what it was, technical are closed on a sunday so thought i would ask on here..

 

[3083sam]

The heating side works fine, only on the hot water side. Thought it might be a stat..

 

[shaky]

Plate h/e

 

[Roger Welton]

If the heating works then as already said blocked plate hex

 

[bennygas]

i think I'd be inclined to agree with all those who're thinking the dhex is a likely culprit.

 

[cdodds2004]

plate for sure!