Hot Water OK but no Central Heating

Hello,

I have a Stelrad Ideal Elan boiler with Honeywell ST699 timer and dial type thermostat.
The timer controls the hot water and heating.
I have a hot water tank in the loft which is filled via the boiler.

When the hot water is selected, the boiler fires up and works fine.

When the heating is selected, nothing happens.
With the heating on, 240V is supplied to the thermostat. With it off, there is no supply to the thermostat.

When the thermostat is rotated to below room temperature one of the 3 terminals goes from 240V to 0V, so I guess that it is working?

The only other thing to note is that a fuse tripped in the house 2 days ago.
The heating failure was first noticed this morning.

Any advice please?
Ian

Your room stat operates a motorised valve which then brings the boiler on. This is the next thing to test.

Is it a 3 port or two 2 ports?

Thanks for your reply Rob.

It is a 3 port Honeywell V4073A1039 valve.
There is a 'lever' on the bottom. I was wondering if this was some sort of manual switch?

http://www.heatingcontrolsonline.co...39-22mm-midposition-motorised-valve-p-89.html
Refering to this image, I am guessing that the water flows in the bottom and is diverted either left or right?

How would I go about testing the valve?

I don't understand how it would cause the boiler to switch on.
Is there an output from the valve to the boiler?

Thanks again.

It is the motor on the valve that is faulty.

I get 240V on the motor terminals but no motor movement.
Manually activating the valve with the motor removed makes the heating work.

Thanks for pointing me in the right direction.

Just to complete the sequesnce
- the power goes from the timer to room thermostat
- when the room thermostat needs heat, power goes from the room thermostat to the valve motor (actuator) to turn "on" the "CH"
- When the actuator turns the valve to CH direction, it flips a micro-switch which connects power to the boiler & pump, which leap into action.