Intermittent burner lockout on a Vaillant Thermocompact

[Kumquat]

I had a Vaillant Thermocompact boiler fitted last October- it was the only model still available to be installed in our communal flue (a SE Duct). A couple of times over the winter I found it had locked out with fault code F29 (something about the burner going out and not relighting quickly enough)- both times it was blowing a gale at the time so I figured maybe that created some unusual draft in the flue. Since May, it's locked out in the same way a total of 7 times, three times this week. Now I know it's a been a bit breezy this week but really.....! It's only running an hour in the morning and an hour in the evening to heat the water at the moment so that makes the odds of it locking out pretty high recently - and a lot higher than in the winter when I was running it 11 hours a day.

The engineer that came under the warranty said he thought that there's nothing wrong with the boiler, it's something to do with the flue, shrugged and left. Not very helpful. Do the professional amongst you think that sounds likely? I never had any problem with my previous elderly boiler, I only changed it to get a more efficient one. Now it seems I wasted £3k.

 

[bengasman]

What was the reason that you didn't get a high efficiency boiler? I know it is not related to the problem, just curious.
If the vaillant chap knew what he was doing, the only thing you can't really test is the pcb, which you could have replaced as a last resort.
As you are pretty clear it depends mainly on the presence of absence of wind, it seems more like a flueing problem.
Am I correct guessing that you have the model without a fan?

 

[Kumquat]

Apparently this was the only model that could be used with a SE Duct. Not as efficient as a condensing boiler but better than my old one I was told.

I don't know if it has a fan to be honest - it's a 628E if that helps? It sounds like it's running something while the burner is alight (over and above the sound of the pump). Excuse my ignorance but what's the pcb?

My installer told me that Vaillant technical suggested it could be the gas pressure switch/sensor but the guy that came didn't test that, he just said 'F29 on a Thermocompact is always the flue', stuck his emissions meter in the hole, said that was ok, told me the flue might be partly blocked and left. I thought- well, given that wind is a factor then maybe.... But my question is, if that's the case, why is the problem worse now than in the winter (when let's face it, it was windier on average) and why is it getting more frequent? (Four of the last seven lockouts in the last two weeks).

 

[bengasman]

Printed Circuit Board is the bit that controls the whole boiler. Why it is more than before is anybody's guess without seeing it.
Worth contacting the freeholder (in writing ) and informing him there is a problem with the flue duct and ask for proof it is in good working order.

 

[picasso]

the thermocompact requires an adaptor on the flue for the se duct, I would get that checked as well .

 

[simond]

Supplier gas pressure is often lowered in the summer. It may be just as Vaillant suggest.

Blocked SE duct is unlikely because everyone else would be experiencing problems. In any case, blocking a SE duct takes some doing.

 

[Agile]

Using an SE duct for a modern boiler is not my preferred solution but I appreciate that there may be reasons why an alternative position for the boiler could not be achieved.

However, I would be very surprised if there are no other boilers fitted in your block which are not using the SE duct.

The next question is to your installer to see if the SE duct adapter has been fitted!

I do have to say that contrary to your opinion, yesterday was VERY windy in the NW London area!

Tony