Hot water comes on but no central heating

[chenojoe]

Got a bit of a strange one. I have the Hive control system which is connected to quite an old Ideal Classic boiler.

When I turn on the central heating via the thermostat the control light indicates the heating should be on but the boiler does not fire up. However if I turn the hot water on the boiler lights for the hot water straight away.

The only way I can get the central heating back on is to turn the boiler off and on fully. It will then work for a while before repeating the situation above.

Any idea why this would happen as if the boiler was faulty surely it would not light?

Many thanks

 

[Justin Passing]

Expect you have a Y plan system then??
Single 3 port valve?

 

[ianmcd]

its not a boiler fault, as already correctly advised will be a controls fault external to the boiler