Hot water but no Heating

[Lunarmodule]

Hello people,

Just wondering if anyone could shed some light on my problem.

I have a fairly old system, gas fired Ideal W2000 boiler and a Comet 2-130 pump. with ACL Drayton Thermostat, and ACL LP-522 Control unit.
(Gravity tank)

4 radiators up-stairs, 4 downstairs.

As it wasn't working my first thought was the thermostat so i replaced this and all was fine and dandy it worked. When i came to switch it on today nothing i here the click from the thermostat but nothing from the bolier.
So i went out and bought a new control unit (ACL LP-522). But again nothing, Checked the gravity tank which was low but is now full, tried again nothing all the radiators are bled and the hot water is fine and the pump is fine too.

Please help i'am a novice with central heating, but ideas are running out.

Thanks in advance

 

[Nixt]

If pump runs, controls OK. If dhw hot, boiler OK. Check for heat past pump unless very hot pump is faulty. If pump makes a noise and gets warm doesn't mean its working.

 

[gas4you]

When you say gravity tank, do you mean it is a gravity heated hw cylinder? 4 pipes offthe boiler?

If it is pumped (2 pipes off the boiler) then it could be the heating zone valve needs the head replacing.