Vaillant Home System 15 - F.28 Intermittent fault even after many parts have been replaced

[akz786]

Hello everyone,

I'm seeking advice on a persistent issue with my boiler. Since January, I've been dealing with an F.28 error code on my Vaillant Home System 15 boiler, which requires me to reset the boiler to get it running again. Here's a summary of the repairs and checks that have been done so far by British Gas on home care:

• Replaced: Main Gas Valve, PCB, Ignition Electrode, and Spark Ignitor
• Cleaned: Condensate (no issues found)
• Checked: Gas flow at both Mains and Boiler

Despite these efforts, the boiler still takes several attempts to ignite at times and rarely ignites on the first flame. BG have tried to systematically work around this by covering and replacing items mentioned above and checked Gas pressure and all else is OK.

The F.28 code will of course trigger after 5 failed attempts so this happens intermittently but will occur a few weeks to a month at a time.

Just wanted to know if there was any guidance or opinions on what else could be causing the multiple ignition/flame detections - even after replacing the electrode and parts mentioned above?

Could it be something associated with the main heater exchanger?

Any help would be greatly appreciated!

Thank you.

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[CountryFan]

Is the boiler under warranty? How old is the boiler? I don't think the spark ignitor is a spare so maybe the HT ignition plug? Do you know where the condensate flows to?

 

[numpty1]

dodgy earth on house/boiler electrics......?

 

[akz786]

Is the boiler under warranty? How old is the boiler? I don't think the spark ignitor is a spare so maybe the HT ignition plug? Do you know where the condensate flows to?

No unfortunately not, its 6 years old now. Forgot to mention the HT ignition plug was replaced as a part of the Electrode.
Good point on condensate exit, its hidden as its a new build, as its next to the rear main wall its probably exiting to where the outside hose pipe drain is adjacent to the boiler.

 

[akz786]

dodgy earth on house/boiler electrics......?

I very much doubt so being a new build, everything else works spot on.

 

[CountryFan]

Good point on condensate exit, its hidden as its a new build, as its next to the rear main wall its probably exiting to where the outside hose pipe drain is adjacent to the boiler.

New builds are a pita unfortunately. I've seen some poor installs on these, you may have a belly in the condensate pipe that could be causing an issue (similar to that of a frozen condensate pipe). If everything else has been replaced and it's not a sticky regulator at the gas meter, I'd be looking at this (condensate).

 

[akz786]

New builds are a pita unfortunately. I've seen some poor installs on these, you may have a belly in the condensate pipe that could be causing an issue (similar to that I'd a frozen condensate pipe). If everything else has been replaced and it's not a sticky regulator at the gas meter, I'd be looking at this (condensate).

Thats a good shout I can certainly double check that although the trap was clean and water was flowing out decently.

My curiosity is more around ignition attempts still taking 2-3 times, even after all those parts have been replaced.

 

[Harry Bloomfield]

Do you have any other gas appliances, close to the boiler location, which you could light, and check what happens to the flame, when the boiler attempts to ignite?

 

[ScottishGasMan]

So it only locks out to F.28 every week to month, but are you saying it almost always takes 2-3 goes to ignite and run?

 

[akz786]

Do you have any other gas appliances, close to the boiler location, which you could light, and check what happens to the flame, when the boiler attempts to ignite?

Just a counter top gas cooker -I could try and test that and see what happens

 

[akz786]

So it only locks out to F.28 every week to month, but are you saying it almost always takes 2-3 goes to ignite and run?

Yes that pretty much a common scenario from my logging so far, however the parts changed so far should have ensured the ignition attempts are at least 1st if not second most of the time.

 

[Harry Bloomfield]

Just a counter top gas cooker -I could try and test that and see what happens

It will help confirm if the pressure is dipping, when the boiler is trying to ignite.

If the gas is getting through, ignition should be instant. My Vaillant does a purge cycle, then ignition and never fails to ignite on the first attempt.

Your problem, must be either gas or an ignition failure. Does it ever bang, when it does ignite?

 

[akz786]

It will help confirm if the pressure is dipping, when the boiler is trying to ignite.

If the gas is getting through, ignition should be instant. My Vaillant does a purge cycle, then ignition and never fails to ignite on the first attempt.

Your problem, must be either gas or an ignition failure. Does it ever bang, when it does ignite?

So the BG engineer from what I saw did test this pressure at the boiler and the Gas meter whilst using the P.01 program at 0% to 100% to ensure the pressure was correct and OK. He advised me it was.

Yes it does make a slight bangon ignition attempt 2/3 or even 4 for that matter.

 

[Harry Bloomfield]

Yes it does make a slight bangon ignition attempt 2/3 or even 4 for that matter.

That suggests to me, that the gas is there, and that it is an ignition fault.

 

[ScottishGasMan]

however the parts changed so far should have ensured the ignition attempts are at least 1st if not second most of the time.

Only if one of those parts was faulty. If those parts were ok then I'd expect the boiler to run the same as it did before.

Have they ever carried out a full strip service of the unit? Taking the burner housing off and washing through the heat exchanger?