Halstead Ace High DHW but no CH

[ben phillips]

Hi All,
Having a problem with my CH the boiler just does not respond to a demand for heat, but the DWH has no problems. The only way I can get boiler to fire up and run ( for around 10 seconds ) is to disconnect the dhw sensor ( thermistor ) as soon as I re-connect the sensor ( within the 10 second period the boiler shuts down ) would this point to this item being faulty.
Any help would be very much appreciated
Ben

 

[ranger1]

Test the resistance on the thermistor, check with manufacturer what it should be, normaly 10 ohms, but check

 

[ranger1]

Forgot to mention tempreture will affect the resistance, so check

 

[black 31]

just thought but i think when demand is removed by disconecting thermister there is an anti cycle mode which prevents the boiler from firing in ch mode
for about 3 or four mins seemsd a lot longer when you stood waiting