Ravenheat HE85(A)T Combination Boiler Burner On/Off

[Metalpolish]

Can anyone help...What part needs replacing and what test can be carried out....
Problem
Deman for Central Heating (CH), Burner lights, for 3 sec, reduces flame for 3 sec, then turns off, then starts trying to light again.

If DHW turned on, wait until water hot from tap, turn off DWH tap, 3 way valve turns over to CH, burner keeps on until water hot enough, then starts the problem cycle.

Settings are;

Inlet gas pressure
Static no flow - 21 mbar
Full gas flow - 19.5 mbar (10.5mbar at burner)

CH Demand
Signal to modulator - 5volts no gas at burner - Burner off
Signal to modulaor - 20volts 4 mbar gas at burner - Lights & stays on for 3 sec
Signal to modulaor - 16volts 2 mbar gas at burner - Lights & stays on for 3 sec
Signal to modulaor - 0volts 0 mbar gas at burner - Burner goes out

DHW Demand
Signal to modulator - 5volts no gas at burner - Burner off
Signal to modulaor - 20volts 4 mbar gas at burner - Lights & stays on
rises to-
Signal to modulaor - 34volts 10.5 mbar gas at burner - Lights & stays sec
Signal to modulaor - 0volts 0 mbar gas at burner - Burner goes out
Recycles ok


Many thanks to those that can help......

 

[Agile]

Sounds like another fan PCB failed!

Although you have described it rather differently from most people.

Tony

 

[Metalpolish]

Tony,

Many thanks for the help, it is very much appreciated........

I also hope this request for help and your answer will help others.....

I will post a reply to let you know how it goes....

Once again many thanks...

David.

 

[Metalpolish]

Hi All,

Replaced Fan Modulating PCB, burner now stays on when CH requires heat.

Once again many thanks to Tony for advice.

David