Baxi 105 HE - Hot water cycling

[Riknos]

Hi All,

Having a nightmare with my boiler. Hot water cycles - get's really hot, scorching hot, then cycling to luke warm, back to very hot. Burner effectively cuts out for 10 seconds then fires back up then does the same again after a minute. This only happens with hot water, CH runs fine (although I only have CH temp turned up to 2/3 max, any higher the radiators are too hot to touch) so may well do it for them also?

The parts I've had replaced in the last few weeks are:

• PCB (this was 12 months ago actually)
• Diverter valve removed, cleaned, diaphragm check and ok. Front and back nut thingys replaced and regreased - pin moves freely (this was leaking from the pipes at the bottom for a while, but this leak has been fixed now and doesn't anymore)
• Primary heat exchanger cleaned & re-fitted
• Plate heat exchanger cleaned & re-fitted.
• New DHW temp sensor fitted
• Central heating system has been filled with Fernox F2 and flushed.
• Boiler has been serviced.

Any ideas what else it could be?

I actually have a different looking diverter valve than I think I should on the 105 HE

Mine looks like this:

Whereas when I ordered the part for the diaphragm, it came for this one - which every time I google the 105 HE they seem to have this fitted instead:

So not sure if the wrong part has been fitted at some point? (lived here less than 2 years) Or if this makes a difference?

Any advice much appreciated - thanks.

 

[cross thread]

looks like the valve off the instant,your issue may be gas related as the boiler may not be modulating ,get a engineer in with the correct test gear

 

[ianmcd]

yours is a Baxi 105HE instant not a 105HE they are not the same boiler

 

[gas112]

Providing plate has properly been cleaned then as has been said sounds like modulation ,low on gas valve will be set far too high

Edit
What is hot water demand light doing when tap on is it steady or flashing

 

[Riknos]

Providing plate has properly been cleaned then as has been said sounds like modulation ,low on gas valve will be set far too high

Edit
What is hot water demand light doing when tap on is it steady or flashing

Hopefully plate has been cleaned well enough. Perhaps I should just get a new one?

When hot water demand the light is steady no flashing. No warning lights at all. All temperature lights did flash occasionally but this was before any parts were replaced