Vaillant Combi Boiler - F28 fault

Hi All

Possibly someone can give me some info/help about my boiler as no one at Vaillant technical department has offered a response from email and when I called I was told the call out fee excluding parts would start at £275. The boiler is just over 5 years old and has worked fine for years. I think it is part of the 828 range (that is the installation manual I have for it).

Anyway I always put my boiler on timer and everyday it comes on fine. However the first day of snow it didnt. This day also just so happened to co incide with me bleeding my bathroom radiator the night before. After bleeding the radiator the pressure dropped to zero and I refilled the pressure back to 1.5. and all was working fine.

Next morning the heating did not come on with the timer. The boiler flashed F28 and pressure was down to zero. I refilled pressure to 1 this time and pressed re ignite button. Boiler lit up straight away and was fine. As well as that once it got going the boiler pressure than rose to 2.5 (the missing 1.5 of pressure seemed to come back from nowhere???).

The problem i have now is when the boiler turns off (on timer) the pressure slowly drops and boiler will not come on unless i go through the above procedure again. I now have to keep turning up and turning down the temperature at night to use the boiler, so I dont have to wake up every morning with a boiler thats flashing red.

It was cold before the 1st night of snow (dropping below zero for a few days) but the boiler was working fine on timer so I am not sure if its the cold or the fact that I bleed my bathroom radiator that seems to have created the problem. I have had no problems re igniting the boiler when it does switch off and pressure drops. And like I said the pressure always jumps up to the amount I have just added + what it was the day before once it gets heating.

Any ideas what the problem could be and what sort of cost I am looking at?

Any advice appreciated

Could be frozen condensate pipe

Bit of advice from a novice you have a leak at a radiater or somewhere hence the pressure drop also it maybe that Pressure relief valve the 15m pipe just under the boiler going straight out.. To eliminate the pressure relief valve wrap a carrier bag around the pipe outside so if any water leaks it collects in the bag and if the bag has water the you need a new pressure relief valve

so you bled it while it was warm?
and then refilled it and wondered where that 1bar went when it cooled down and all the water contracted?

F28 is... a gas problem..

No gas; Isufficient gas; Incorrect gas valve
adjustment; Electrode defective; Ignition lead defect;
Electronic igniter defective

Click to expand...

leave it on overnight is the simple answer until after x-mas so you don't have to pay for reduculous call out charges..

F22 is what i was thinking my apologies i'll leave it to the experts..

thanks for the answers. I have no real knowledge of boilers so if my responses seem completely ignorant I apologise but here goes.

Firstly the pressure relief pipe - I am guessing this is the pipe that runs from underneath my boiler to my washing machine waste pipe (both boiler and washing machine are in my utility room).

The pressure in my boiler does drop off when the timer switches heating off over night but goes back to its original pressure or higher when switched back on. So basically if the timer goes off at night and just before going off it had 1.5 pressure. During the night the pressure must drop - heating doesnt come on in the morning and f28 flashes The next morning when I manually reignite and put in 1 bar of pressure to do so. The pressure will eventually creep up to 2.5 when its fully heated. So the initial pressure seems to come back. If it had a leak would it not just keep dropping throughout the day?

In regard to condensate pipe I dont have to boil any kettles or anything to reignite the boiler in the morning. I just need to increase the pressure in the boiler and reignite and everything works fine until timer switches off. So I am not sure if something is freezing or not but I dont have to unfreeze anything to power it back up.

Since this problem started over 3 weeks now I have not turned boiler off or onto timer (apart from 2 times) and the pressure is not dropping it generally is staying the same though a couple of times it has hit over 3 bars (from all the manual reigniting and increases of pressure) and I guess the pressure relief has opened and the pressure has dropped because of that.
But it works fine when left on.

ColJack said:

so you bled it while it was warm?
and then refilled it and wondered where that 1bar went when it cooled down and all the water contracted?

F28 is... a gas problem..

No gas; Isufficient gas; Incorrect gas valve
adjustment; Electrode defective; Ignition lead defect;
Electronic igniter defective

Click to expand...

leave it on overnight is the simple answer until after x-mas so you don't have to pay for reduculous call out charges..

Click to expand...

The heating was on the day I bleed the radiator. It was a tall towel warmer type rad and only the bottom half was heating up. The rad was upstairs, I let all the air out but by the time I finished all pressure was gone from Boiler and it had switched off and flashed F28.

I am happy to leave it on all night but I am going away for a few days over xmas and want to put it on timer during that time really.

In regard to F28 flashing - thats what comes up on the screen. But if I fill pressure hit ignite it all works fine. The pressure is always down to zero by the morning if I let it turn off on timer at night. But like I say this has only started since first day of snow and me bleeding radiator which happened to be the same day. All year it worked fine on timer mode.

expansion vessel needs recharging and pressure relief valve replacing. Once thats done see if anything else rears its head.

mickyg said:

expansion vessel needs recharging and pressure relief valve replacing. Once thats done see if anything else rears its head.

Click to expand...

I am not going to ask what that involves or even means. But what sort of cost is involved in that and how long should it take.

The pipework that runs from the pressure relief valve to washing machine waste pipe was only fitted about a year ago. Could that have damaged the valve? The boiler is definitely releasing pressure on the occasions I have filled it to high (from too many manual re ignites).

Not sure what the expansion vessel is or does but from a general physics point of view I always thought the problem might have been related to the changes in water density when hot and cold as I am sure the system is not leaking and pressure does not drop when its left on. Does the expansion vessel control this?

The pressure of the water changes when it gets hot and that is adsorbed by the expansion vessel.

Yours is failed or might just need recharging. You could try to do that yourself if you read the FAQ on this site.

The PRV may well NOT need changing as its only doing its job of opening when the pressure becomes excessive.

We usually charge just over £100 to replace the PRV and service the boiler in our local area.

Tony

Agile said:

The pressure of the water changes when it gets hot and that is adsorbed by the expansion vessel.

Yours is failed or might just need recharging. You could try to do that yourself if you read the FAQ on this site.

The PRV may well NOT need changing as its only doing its job of opening when the pressure becomes excessive.

We usually charge just over £100 to replace the PRV and service the boiler in our local area.

Tony

Click to expand...

Hi Tony

Thanks for the info. If the expansion vessel needs replacing and cannot be sorted by recharging what does that normally cost.

This sounds to me like its the problem. I am not a fitter/plumber so is it ok for me to attempt the recharging of the vessel?

Many thanks for your help

You can try to repressurise it yourself but must follow the instructions in the FAQ.

If it has failed then it usually means the boiler has to come of the wall and that is often not far short of £200.

Sometimes its possible to fit an external EXV and thats much cheaper, perhaps about £90.

Tony

adamhayes said:

F22 is what i was thinking my apologies i'll leave it to the experts..

Click to expand...

I'm not an expert, I just happen to have the same boiler and a copy of the manual..

Agile said:

You can try to repressurise it yourself but must follow the instructions in the FAQ.

If it has failed then it usually means the boiler has to come of the wall and that is often not far short of £200.

Sometimes its possible to fit an external EXV and thats much cheaper, perhaps about £90.

Tony

Click to expand...

That's scary

is your boiler in a particularly cold area?

with the snow comes the very cold..
if the ignition sensor is very cold it might not register the flame heating it fast enough before the controls think that it's not lit???

alternatively, with the snow comes cold damp air which at night might hinder ignition ( whilst on the flame chamber and flue would warm the combustion air possibly? )

also there's the posibility of snow on blocking the air intake ( warm during the day preventing snow from accumulating, cooling at night letting it stick and block? )


Please note that all of the above are just musings of someone with a similar boiler and not an expert..