Faulty hot water on baxi 105 e

[sarahs dad]

Hi guys wondering if you could offer me any advice ?
A customer has had a mixer shower fitted not thermostatic, but compatable with a combination boiler ( manufacturers)
hot water is getting hot but boiler is switching off every 40-50 seconds and goes off for about 7-8 secs.
Ive tested both temp sensors for resitance and are correct, gas valve working pressure is 12mbr, cant adjust to 13.4 mbr, but remains steady .
Ive not removed plate to plate heat exchanger but this looks most likely.
Can anyone confirm this ?

 

[kevplumb]

does a hot tap run ok

 

[sarahs dad]

Yes mate tap and flow rate are plenty and when central heating is on boiler runs for a lot longer, untill up to temp.

 

[bengasman]

Sounds like a blocked plate hex.

 

[sarahs dad]

Thanks bengasman, i was 70% sure and don't really do a deal of breakdowns and this guy wont stand parts being chucked at it.
Many thanks again .

 

[bengasman]

Simple test to see if there is sludge in the system.
Run the heating with all the downstairs rads fully open for half an hour.
Feel along the bottom of the rads, and see if the middle is colder than the sides. If it is, move your hand slowly up, in the middle, the higher it takes to get warm, the more sludge. If there is no cold spot in the middle, it could be something else, though still a chance the hex is blocked. In that case, remove the hex and check visually.

 

[powell30]

Nope....your all missing the fact the boiler is working fine other than when shower on.........Cold is at a slightly higher pressure than hot allowing a higher flow rate , the hot water flow through boiler is lower therefore the dhw stat is shutting down the boiler.....get a thermostaic shower compatible with mains pressure. Plate heat ex is fine

 

[kevplumb]

does a hot tap run ok

err

 

[fitz1]

whats the min burner pressure falling to on the gas valve. should be about 2mbr.

 

[sarahs dad]

Fitz 1
you are spot on mate.
Min working pressure at gas valve was 10mbr.
Adjusted it to 2mbr and hey presto boiler stays on, then adjusted max working pressure to suite.
Ended up calling baxi tech and havent got back to site to thank you guys for your assistance.
Thankyou all