Advice on old (and I mean *old*) Vaillant boiler

[Deleted member 98127]

Hi there,
I have a 25-year-old Vaillant CombiCompact 242EH which has developed a hiccup on the heating side, and was wondeirng whether anyone might have some advice - yes, I know, "Get a new boiler!" is the most likely, but it seems like such a small (and intermittent!) issue that I wonder whether it cannot be fixed easily by someone who has some actual experience with this or a similar model and knows what they are doing.
I've had 5 different plumbers in both last March when the issue first arose and this winter, and they've not been able to fix it (the last one was a good 5 years younger than the boiler and seemed rather intimidated by anything that didn't have a digital error code display; he took one look and condemned it on the spot....).
So, the issue:
The hot water side of the boiler runs perfectly fine, no problems. The heating side runs most of the time. Occasionally, however, when the thermostat sends the signal to the boiler to fire up, it just doesn't ignite. Usually there is a first a relay click that starts the pump and ventilation, and then after a few seconds another click, closely followed by the click of the ignition and the "wooompf" of the gas igniting. Sometimes, though, there is the first click, the sound of the pump and ventilation starting, but nothing else. The gas does not ignite, and the boiler just pumps cold water through the heating system. The heating is usually fine to start up first thing in the morning, but then starts acting up in the late morning until the evening. If you keep trying and switch it off and on again a few times, however, it will eventually ignite (though that's really no good if I'm not at home to stand next to the thermostat to do this...)
The several heating engineers who have been here have installed both a new diaphragm and a new diverter valve with no change in the situation (I have a home emergency insurance, so unfortunately they send a different person every time....). It does seem like just the relay needs adjusting or cleaning or replacing, but none of them seemed to know which part might be responsible. I thought it was worth asking whether anyone here has more experience and has come across this issue or would know which part is the culprit, and whether this is fixable - before I start getting in quotes for a brand new boiler...
Thanks ever so much!

 

[jtsplumbing]

Unfortunley we cant give any advise on boiler repairs, these are a good boiler but have lots of small parts used to work on a lot of these when I lived in Berkshire , If I were you get Vaillant out on a fixed price repair if you want to keep this boiler, sometimes its a blockage in the very small pipes around the diverter valve

 

[Deleted member 98127]

That was one of the suggestions I got as to what *might* be wrong, except that they said that hardly anybody (certainly not this guy himself) these days could be asked to do the dirty and tricky job of cleaning them out so it came around to "Just scrap the thing!" again.
It's not like I'm trying to get advice on how to fixy this myself, I just wanted ask whether anyone has come across this issue before so might actually know what's wrong so that the next heating engineer might actually have some clue as to what to look at - or maybe even find someone here who lives close enough that they could come over themselves. I'm a bit loath to spend 250 quid on a Vaillant Fixed Price Repair where chances are I will only be told again that they don't know what's wrong and "advise" me on purchasing a new boiler...
I did find this installers' manual online, would that be of help to anyone for identifying where the problem might lie?

 

[Harvest Fields]

Get an engineer that works on Vaillant’s a lot. He might sort it quicker. Or Vaillant’s fixed repair isn’t bad. But to be honest I would also put the money towards a new one.

 

[plumbandplumber]

- or maybe even find someone here who lives close enough that they could come over themselves.

Maybe a good idea to give your location?

 

[Last Plumber]

That was one of the suggestions I got as to what *might* be wrong, except that they said that hardly anybody (certainly not this guy himself) these days could be asked to do the dirty and tricky job of cleaning them out so it came around to "Just scrap the thing!" again.
It's not like I'm trying to get advice on how to fixy this myself, I just wanted ask whether anyone has come across this issue before so might actually know what's wrong so that the next heating engineer might actually have some clue as to what to look at - or maybe even find someone here who lives close enough that they could come over themselves. I'm a bit loath to spend 250 quid on a Vaillant Fixed Price Repair where chances are I will only be told again that they don't know what's wrong and "advise" me on purchasing a new boiler...
I did find this installers' manual online, would that be of help to anyone for identifying where the problem might lie?

As others have suggested. Find an older (Not to be ageist), Heating Engineer who has worked on those Boilers before. They are a good Boiler, I always liked them anyway. It sounds like an easy-ish repair for the right individual. The Vaillant fixed price is not cheap but it may save you a procession of inexperienced Engineers and a run of part swapping sessions.

 

[Chalked]

Hi
Inside your boiler there lots of mechanical. Hydraulic controlled valves fed by very small capillary tubes. Any one can block up. Trust me , you have a great boiler, but once an engineer starts on this, he will have sleepless nights.

But, there is one thing you can try yourself without contravention of any gas safe regulation. This has worked for me in the past. But may not make any difference to your problem.
Where I have highlighted, there’s a screw. Remove it, then with a very thin flat screwdriver locate the screw hidden inside. Turn this a quarter turn left, or right.
I’m not going into any more detail why. But it’s worth a go.
If that doesn’t help. I’m afraid it’s an older engineer, who is experienced in this boiler. Or a new boiler.

 

[jtsplumbing]

2 other things , that looks like the original pump if that is not giving out a good pressure it will effect some of the other valves, look to the right of red circle the black diff valve is one that fails gets weak again something you can do without compromising the gas rules, Think I've still got some replacement diaphragms for that valve along with a case of other parts

 

[Deleted member 98127]

That all sounds great, thanks a lot for all the good advice!

 

[Deleted member 98127]

View attachment 32752
But, there is one thing you can try yourself without contravention of any gas safe regulation. This has worked for me in the past. But may not make any difference to your problem.
Where I have highlighted, there’s a screw. Remove it, then with a very thin flat screwdriver locate the screw hidden inside. Turn this a quarter turn left, or right.
I’m not going into any more detail why. But it’s worth a go.

So according to the manual that's the re-ignition delay? Not sure whether that's where the issue might lie since the boiler occasionally fails to ignite several hours after the heating was last on....would I be looking to reduce or increase the delay?

 

[Chalked]

So according to the manual that's the re-ignition delay? Not sure whether that's where the issue might lie since the boiler occasionally fails to ignite several hours after the heating was last on....would I be looking to reduce or increase the delay?

Your nor increasing, o decreasing it . Your just moving onto a different contact point. Theses work like old hifi volume controllers and the contact burns out. Moving it slightly makes it contact with a new area.
Worth a try