Vaillant turbomax combi f 28 problem

[jeffwhite]

Last couple of weeks the following happens: Boiler goes to lock out, F 28 fault on display. Manual states no gas, insufficient gas or elecrodes problems. But after resetting the boiler about 4 times it all comes back to life and stays like that for up to 2 or 3 days. Then lock out occurs again, but I repeat the reset, again after 4 attempts or so and it is back to normal. Looks like I could do this indefinitely!
On my own visual inspection - electrodes firing OK (good sparks visible), 240v on the PC board gas valve terminal, gas supply in the house OK.
What is likely to be the cause, before I entrust the problem to a qualified heating engineer ?.
I suspect a slightly blocked gas valve. is there a serviceable filter inside ?or is simply a case of a new valve - full stop.
Any advice greatly appreciated.

 

[gas4you]

Could just simply need the minimum burner pressure adjusting. Also electrodes could probably do with being bent slightly closer to burner, for rectification process.

 

[jeffwhite]

Thanks Dave for your useful advice.
I presume adjustment of the burner pressure is a qualified person job and should'nt take too long. I cannot see anything on the boiler that looks like a DIY adjustment !
Jeff White

 

[gas4you]

When was the last time it had a proper service?

If it was a while ago, then book it in with a reliable RGI. The burner pressure adjustments will be set during a service and yes you are correct that these are not really a DIY adjustment.

There are still other possibilities to what may cause this fault, but without the above basics being checked first, a wrong diagnosis is always possible.

 

[Agile]

Anything to do with gas settings should be done by a qualified person.

These would be checked on a "proper" service but be aware that the BG safety check does not look at them if the flue gases are within tolerance.

I am assuming that the gas never lights at all in your case! ( Rather than lighting and the flame not being recognised. )

As it only happens on the odd day, I would be wondering if the incoming supply is sometimes low or if the meter regulator is sticking.

It might give further clues if you noted the days and times that the problem occurs.

If the meter regulator was sticking then it probably would not stick if the gas cooker was being used when the boiler is started. But that may be rather tedious to test !

Tony

 

[jeffwhite]

About 3 years since last service. Likley long overdue then !
What causes the burner pressure to change over time ? I somehow imagined that this type of adjustment was static for the life of the boiler. Incidentally boiler is a Aua Plus (or is this a turbomax 824 ?),5 years old and mounted in the loft where it does get quite dusty. Is this something to worry about?
Jeff White

 

[gas4you]

Loft installations are nothing to worry about.

The lack of servicing is though.

This boiler should ideally be serviced annually.

Burner pressures can drift out of adjustment over time, I am not clever enough, or pretend to know the intricacies behind this phenonemen, only that it happens on boilers old and new.

The dust in the loft should not be able to get into the combustion chamber as this is sealed to the room.

Get it serviced and take it from there

 

[jeffwhite]

I am delighted that some of you out there have taken the time and trouble to reply with expert advice. Many thanks indeed.
I consider myself a competent and enthusiastic amateur, but of course I will not touch all this gas stuff. However I am intrigued by what the following adjustments mean, all of which are mentioned in the manual -
- Gas inlet working pressure
- Main burner pressure
- Ignition rate
If I could get some idea of what these mean, I will feel more comfortable about seeing what the RGI will be doing when I get him him. This is based on an uncomfortable time some years ago when I believe I was ripped off by an installer (registered). Sorry to those professionals who are genuine and truly competent, but I have a slight distrust.
Apologies
Jeff White

 

[jeffwhite]

I am delighted that some of you out there have taken the time and trouble to reply with expert advice. Many thanks indeed.
I consider myself a competent and enthusiastic amateur, but of course I will not touch all this gas stuff. However I am intrigued by what the following adjustments mean, all of which are mentioned in the manual -
- Gas inlet working pressure
- Main burner pressure
- Ignition rate
If I could get some idea of what these mean, I will feel more comfortable about seeing what the RGI will be doing when I get him him. This is based on an uncomfortable time some years ago when I believe I was ripped off by an installer (registered). Sorry to those professionals who are genuine and truly competent, but I have a slight distrust.
Apologies
Jeff White

 

[Agile]

The burner pressure on conventional boilers like yours is primarily dependent on the internal components of the gas valve which contains a regulating section and a flow adjusting section.

The components inside the gas valve on which the burner pressure is dependent are steel springs and rubber diaphragms.

Thermal cycling on the springs will cause them to slightly change their characteristics over time, often particularly within the first few years.

In addition the electronic components will age on the PCB which control the gas valve modulation causing further possible variations.

It can be quite surprising just how far out of adjustment a boiler can become if they are not checked regularly. An earlier Vaillant boiler had the adjustment behind lead seals and the instruction was not to adjust them without contacting the manufacturers first.

I found one that had drifted from say 10.0 mB to 13.5 mB which is quite significant and verging on dangerous ! I called the manufacturers who of course said they had never heard of one drifting so far before.

Surprise surprise, a few months later they did a recall asking that every boiler should be checked and reset if necessary.

I would not give advice on what could be used to aid DIY gas work. Most can be found by searching forums like this though. Its best if you call a competent RGI and get him to explain to you what they all meand and how he is checking them.

Tony