how to change thermister on ideal isar he35 boiler

[zaccy]

hi,
my boiler is flashing the fault code H3 which i believe to be the thermister (after reading forum because have no manual)
anyone have any idea how to change a thermister on an ideal isar he 35 boiler please.any tips would be greatly appreciated.i think these are only about £30 so would like to save labour costs
many thanks

 

[Agile]

If its the DHW thermistor which has failed then all you need to do is turn off the mains water supply and the power and unscrew the old one and replace with a new one reinstating any seal or sealing washer.

Potentially a very simple repair but as you dont sound very confident it might be better to call someone who can give the boiler a proper service.

I would also say before you order any spare parts measure the resistance of the sensor with the boiler cold to see if it really has failed!

Tony

 

[zaccy]

hi tony,
thanks for replying.
just measured the resistance and its 13k ohm.trouble is ,i dont know what it should be.does this sound about right ?

 

[Agile]

That sounds correct !

Tony

 

[zaccy]

That sounds correct !

Tony

umm,this is whats happening
the h3 warning comes on intermittently and when this happens the pump can be heard running ,the burner led is not lit and it can do this for 20-30 mins or so before stopping.it might not come on again for an hour or so
also the hot water dosnt get quite so hot as usual occasionly.
does this sound like thermister fault and if so can the thermister work intermittently or when its broke its broke.
thanks again

 

[Agile]

Quite often they go open circuit just when they get hot so thats a quite likely senario.

As they are cheap its probably easier to just replace it.

Otherwise just measure the voltage across it and it will go high when its open circuit.

Tony

 

[zaccy]

yep your right ,im replace it,thanks for your help,much appreciated