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Hi Everyone. I have had a boiler installed in March 2020 (a replacement like for like Valliant boiler). It has cut out twice with F20. Valliant came out and state that I have "All" my rads off so the boiler cut out due to over heating. The thing is that not all my radiators were off, most were actually on (open) including a vast area of underfloor heating connected to the same boiler. I am now being charged £98.00 for a call out because they say the boiler was not at fault and it was because I turned off the radiators. They now threaten that if I do not pay the charge they will cancel my full 5 years cover. To be clear, the previous boiler was beyond economical repair and Valliant replaced the boiler within the 5 year warranty. Valliant commissioned the engineer to fit the boiler and now say they take no responsibility for the job done by their engineer. The guy that came out came in a valliant van and suited in their logo clothing, yet they say it was not their engineer who did the job.

1. Can they do that? Deny responsibility and cancel my 5 year cover because I refuse to pay because the unit is under warranty, 3 months old and at no point informed that I would be charged until I got the letter?
2. How can I constructively challenge this?
3. He did not check all the radiators and simply assumed "all" the radiators were off.
4. Under the terms he should have said the call out was not in line with the warranty and therefore a charge would be made - however, he did NOT state that it was chargeable.
5. I cannot find anywhere on all forums that the boiler will go in to F20 if the rads are off, it does not appear to be associated with the code F20.
6. Any advice from you guys would be welcomed

Thank you
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Staff member
S. Mod
Gas Engineer
Do you have an auto bypass fitted also did they happen with just the ufh on for a few hours ?

f20 is lack of circulation/ over temp
Hi Shaun - thanks for getting in touch. No idea on the bypass. Underfloor heating comes on in the evening only

My concern is that the engineer has guess the problem, assumed incorrectly the rads are all off and charging, without the problem being sorted


Gas Engineer
Can you post some pictures?
I assume you have some zone valves to control radiators and UFH water?


Gas Engineer
vaillant only guarantee the boiler not your system .,
you have poor flow that will need sorting.
I would suggest you get the installer back and properly set up the system, get rid of trapped air and check it has been correctly power flushed.
Hi all.
I suddenly got an email today from Vailiant saying the charge is cancelled and no further action. I guess they accept that the charge was incorrect based on "All" the rads off when they were not. If the problem occurrs again I will have to notify them and will state the advice here form you guys. Thank you so much. It has been a great help

7 th July, 2020

Dear Mr Latchman
We attended your property on the 24th June, 2020 to a report of F20 showing on the boiler display. Our engineer found that all the radiators in the property were turned off whilst the heating was on and this is causing the F20 overheat code. A water sample was taken and sent off for independent testing. A manufacturer’s code was added to your account to indicate an external issue. An automatic charge for attending a non-boiler fault was issued. We have now cancelled this charge and removed the code from your account. We trust this information is of use to you.

Last Plumber

Gas Engineer
Advent Win
Was the original boiler beyond economical repair within 5 years because the thermal fuse went open circuit?
Was the original boiler beyond economical repair within 5 years because the thermal fuse went open circuit?
hi, there was a leak in the boiler from the flue when it was first installed, the boiler was quite corroded and led to a number of parts failure. The matter has now been resolved as per my post earlier

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