Worcester 240 combi RSF

[1966bezer]

The fan on my Worcester 240 combi RSF will not start up half the time. The strange thing is that is you check the brown wire going to the motor on the fan with a volt meter you first get 240 volts then nothing and then the boiler will work. I think that the motor in the fan is on it's way out as both circuit boards have been changed which didn't resolve the problem but the electrical test get's it working for a short time. Has anyone had this problem as I don't want to change the fan and find it something else.

 

[Worldbuilder]

hi bezer. Have you checked the air pressure switch for correct operation. If you are only sometimes getting voltage to the fan, it could be that the switch isn't proving that the fan has stopped when the demand is off. If if fails in the positive side ( Normally Open marked NO ) then the ignition board will not send voltage to the fan until it has proven closed ( NC ). If that is the case it could be water vapour in the pressure tubes ( common fault ) or a perforated switch diaphragm / spring fault in the air pressure switch.

 

[Kristoflampie]

These Worcester fans have a speed control resistor?( I think thats what it is) on the fan itself, on heating the fan starts on high drops to low and then fires if air pressure switch has been satisfied on high speed and drops out on low . If this resistor is faulty the fan stops instead of running on low speed but as its already recognised that the air pressure switch has dropped out on low speed it will go through ignition process with no fan running!! It will then either lock out or the flame will be all over the place for a short period.......... not good!! Either way the fan comes with this low speed resistor fitted . Does the boiler fire okay on hot water?? as the fan runs on high all the time for hot water and will require 240v to do so.
Hope this helps as I have come across it a few times