ravenheat cs 85 no hot water

[julesverne]

posted this in the open by accident so posting here again apologies.

hi guys hope some one can point me in the right direction.

went to ravenheat cs85 today. central heating works fine.

when you turn on hot water it cuts out.

tested microswitch with the multimeter and thats working ok. it was 5.30 so couldnt phone ravenheat tech support
went to test the dhw thermistor and this seems ok on multimeter steady reading but as i disconnect it the hot water fires up into life and then dies as i reconnect it after testing.
with the dhw thermistor disconnected the hot water works as normal but i'm assuming there is no regulation of temperature so i have left it connected for fear old dear may scold herself.

could it be a faulty thermistor or am i missing something.

yes i should rip it out but its an old dear not much money and otherwise its a good working boiler.

 

[diamondgas]

Are you saying the boiler fired with no demand or did you have the tap running, boiler on, at the time you disconnected the thermistor lead? I'd certainly be going with a replacement thermistor and take it from there!