On Friday, 4 November 2016 23:36:43 UTC, Tim+ wrote:
Tim+ wrote:
rick wrote:
On 04/11/2016 19:17, Tim+ wrote:
rick wrote:

Does your boiler have a similar system? I suspect that they've all moved
over to "single stage" ignition of the main burner but you never know...

Tim



Single stage I think ... no pilot flame ... just straight electrode for
ignition along with a flame failure detector.


I asked same Q ... on DIYnot forum ........ and have 2 guys who state
this is an obvious fault, simply fixed - known top all (except the 9
Gas Safe Techs who have been to my place presumably) but they are not
prepared to tell me what it is - even though I will not be touching gas
myslef.


Ah, *******. Dontcha just luv 'em? ;-)

Getting back to your boiler one would imagine that it would have a "purge"
phase following a failed ignition to prevent enough gas building up to
cause an explosive ignition. Still makes me wonder if your gas valve is
bypassing gas slightly resulting in gas build up in the combustion chamber
before the next ignition sequence.

It does sound though as if there must be another fault too to explain the
ignition failures.

Tim


On further reflection, it may be the the gas valve as well as leaking
slightly isn't passing enough gas when it's supposed to be open to get the
gas mixture right for ignition. All in all I would have thought a
replacement valve was the obvious next step.

(I should add I'm not a gas fitter, just interested in how things work, or
ought to work).

Yes faulty gas valve could cause problems.
Normally, gas accumulations in the boiler are flushed away in the pre-purge part of the cycle. So it would have to be a big leak.

Gas explosions can be caused if there is too much air/insufficient gas in the mixture.
So partially blocked gas jet can cause this problem.
Usually just wire brushed and poked clear with a bit of wire.
May not be apparent during normal operation if boiler is oversized (quite common)