Engineer Replaced Parts On Potterton - Still Faulty - SOS

[seniorservice]

Just spent £300 on a repair for a HW fault on my Performa 24HE combi. The problem still persists, although it seemed OK until the engineer left. Diaphragm and heat exch. replaced.

This is a follow-on from a post about this fault I made a few days ago. If I give the symptoms, can someone give me some idea of the fault?

The symptoms are;

With boiler control on hw only, I run the hw tap for approx 5 mins. The water is hot to start, then cools a bit, then starts running cold. When it runs cold, the flame failure flashes, and burner on light extinguishes. The flame failure light keeps flashing for a while, then the boiler tries to start, and the burner on light comes in for a few seconds, before going out again and the flame failure light starts flasing again.

This boiler keeps going like this then, flame failure flashing for a minute or two, boiler tries to start, then back to flame failure, whilst no hw during this.

I then turned the control to hw and ch, but the flame failure just keeps flashing. If I reset the boiler, then turn knob back to hw and ch, then the ch comes on and the hot taps work for a while.

This problem, which my engineer seems to be running out of ideas for is driving me nuts.

Any ideas gratefully received.

 

[kevplumb]

first thought is get him back

 

[gas4you]

Has he, hopefully before he done all this work, checked the basics, ie the burner pressures?

 

[Beerlover]

Has he checked the venturi in the fan and what colour are the ntcs? Also what is the condense trap like - (clean and not backing up)?

 

[jtc21]

Sounds to me like the low rate burner pressure is too low

 

[seniorservice]

Thanks for your help, really appreciated. Sounds like one thing I can check, and a few suggestions for the engineer. He's starting to struggle with it, and won't be back 'til Wednesday.

By the way, what are ntcs?

Keep the suggestions coming.

 

[Beerlover]

ntc = temperature sensor - the later ones were white. Any other colour and I would suggest changing them.