URGENT F.20 after refilling central heating system

[milleniumaire]

Today I partially emptied the central heating system (1st floor and loft) so that I could disconnect an old towel rail and install the pipe work ready for the new towel rail. All went well and I have two capped pipes sticking out of the wall where the new towel rail will be fitted.

Having re-filled the central heating system, the boiler is playing up and refuses to heat the water or the radiators. I noticed it was giving an S.54 message, but after turning off and back on it is now displaying F.20. This has been going on for about an hour now.

There's a lot of splushing sounds going on in the boiler, so I guess there's some air in the boiler, but the pressure is at 1.4 bar.

The boiler is a Vaillant ecoTEC plus 637.

Any thoughts on what the issue might be and how I can get it back up and running? My gut feeling is that the air needs to be purged from the boiler, but I'm not sure how to do that.
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So, I found an article about running the P.0 test purge program on vaillant boilers after the system has been re-filled. Although the article related to F.76 fault codes, the advice for running the test purge program was to purge air from the boiler whenever the system had been emptied and re-filled.

Unfortunately it didn't make any difference. Tried turning off and back on again but I can now hear "kettling", so I've turned it off and will have to wait until Monday to get my heating engineer out to look at it unless someone can suggest something I can do to clear the air from the boiler.

 

[ShaunCorbs]

Air lock need to keep the pump running for a bit to shift it

 

[milleniumaire]

Air lock need to keep the pump running for a bit to shift it

Thanks Shaun, yes I'm pretty sure it is air. How do I force the pump to run without heating water, which then causes the F.20 error?

 

[ShaunCorbs]

Turn the heating on and turn the temp down to off if the pump goes off flick the temp back up then down again easier than going into the settings

 

[milleniumaire]

Unfortunately turning down both the radiator and hot water temperatures and turning the boiler on doesn't work as it eventually gives an F.20 error again and turns off. There doesn't seem to be any way around this other than running the P.0 test purge program, which is turning the pump on and off. I've now run this 4 times, but the boiler still gives an F.20 and there's still lots of noises going on.

I've had this boiler/system for 10 years and over that time have emptied and re-filled a number of times without this issue even though I followed exactly the same steps as I have always done to empty and re-fill.

It is very frustrating, but at least it's not the middle of Winter so heat isn't an issue, but hot water in the morning will be, although we do have an immersion heater on the hot water cylinder, although I've never had to use it!

 

[ShaunCorbs]

Do you have a drain off on the supplies to the boiler ?

 

[milleniumaire]

Hi Shaun, yes there's a drain off on both the supply and return pipes into the boiler. I was thinking of opening the supply drain point and the filling loop, which is on the return side, in the hope that it would flush the air through?

However, having again tried your suggestion of turning the heating/hot water down, as well as running the P.0 test a couple more times and increasing the pressure from 1.4 to 1.6 bar, the boiler now (finally) seems to be working and is currently heating up the hot water cylinder.

I see what you mean about keeping the temperature down as the boiler operated the pump but didn't heat the water.

The other thing I did (and I know I shouldn't) is take the front off the boiler to check the automatic air vent. To my surprise this was fully screwed down! Not sure why or how as normally only the heating engineer opens the front whenever it is serviced! I've unscrewed it 1 turn and a small amount of air came out, but not enough to fix the issue.

Fingers crossed it will continue to work now that the air has been purged.

Thanks a lot for your help.

 

[Aquarius]

Are both flow and return open under boiler? If you’re unsure post a photo

 

[milleniumaire]

Are both flow and return open under boiler? If you’re unsure post a photo

Hi Aquarius, thanks for posting. Yes I can confirm both flow and return under the boiler are open. I don't usually play around with these valves when I'm draining the system as I have drain points on both the supply and return pipes near ground level, which is lower than the boiler and lower than the ground floor radiators (there's a step down into my garage where the boiler and pipework is located).

The boiler is working perfectly again now, so I guess the air lock has been expelled. I've had the heating turned up a bit this morning to get hot water circulating. Time to bleed the radiators again......

 

[Ric2013]

The other thing I did (and I know I shouldn't) is take the front off the boiler to check the automatic air vent. To my surprise this was fully screwed down! Not sure why or how as normally only the heating engineer opens the front whenever it is serviced!

Not necessarily. CBA to check your boiler manual myself, but some boilers have a front cover that is essentially an electrical and mechanical enclosure rather than an intrinsic part of the air or combustion system and, if this is the case, then it may not be strictly illegal for you to remove it.
Auto air vent is probably there for filling purposes only and probably correct to have it shut during normal use. They aren't always reliable and a leak inside a boiler where they are not inspectionable on a day-to-day basis is not desirable.

 

[milleniumaire]

Auto air vent is probably there for filling purposes only and probably correct to have it shut during normal use. They aren't always reliable and a leak inside a boiler where they are not inspectionable on a day-to-day basis is not desirable.

I guess that explains why it was screwed down. I'll be seeing the heating engineer in October when he comes to work on the system, so I'll ask him about the AAV, but I suspect he'll say the same as you and confirm that he screwed it down.