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Plumberpro, Home Appliance Technician
Category: Appliance
Satisfied Customers: 634
Experience:  Heating and hot water heating appliances experienced
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Vailant 618 system boiler F20 fault , it is comming again

Customer Question

vailant 618 system boiler F20 fault , it is comming again and again every couple of days
pump was replaced and it didnt help
what can it be ?
I got Underfloor heating approx 110m2 + 5 small radiators 800x500 on 1st floor
boiler is not new but fairly new
I got Magna clean
Submitted: 2 years ago.
Category: Appliance
Customer: replied 2 years ago.
house is extremely well insulated , so it is taking no time to heat up entire ground floor under floor heating ,
boiler is not new so I am not sure is it an issue with the boiler it self or with installation as from what I read it is about return water coming back to hot to pump
I have set up flow at 58C so it is not to hot
Expert:  Plumberpro replied 2 years ago.
Hi , does the system have an external bypass valve?
Customer: replied 2 years ago.
Nothing i know about. I have manualy opened motorised valve from hot water. So it is open at all time.
Customer: replied 2 years ago.
I tohought to make on the loft next to boiler small loop with one radiAtor to help. But not sure if it will solve the problem
Expert:  Plumberpro replied 2 years ago.
That should aCt as bypass. F20 can also come up due to an issue with the condensate trap.
Check the trap is clear and the water is flowing away easily. Check the wiring to the trap is secure.
You can disconnect the trap wiring and insert a link wire to check there is no fault to the trap float switch.
Customer: replied 2 years ago.
boiler still have the same problem. I got a feeling that before its getting in F20 fault boiler is becoming more noisy
when after reseting boiler I have set the temperature to 75C boiler when in to fault F20 just after 2h
Expert:  Plumberpro replied 2 years ago.
Hi , just checking king the manual for f20 fault code. It say overheat triggered. This could be to a faulty temperature sensor, ie the flow or return etc sensor. Both of these are relatively cheap and easy to change so definitely worth changing these. It also says about ignition fault possible, check leads in good condition and no black deposits on ignition cable and ignition plug,