Central Heating problem with Glowworm Ultimate 40 FF

[leehin]

Within the last week, my central heating has stopped working. The hot water is working ok: both from programmer/timer and manual override. When the hot water is switched on at the programmer, the boiler fan starts up, the ignition lights up, and the water is heated without a problem and to temperature.

The boiler is a Glowworm Ultimate 40FF gas fired boiler with [Drayton/Invensys] acl Lifestyle LP241 timer/programmer

Regardless of the room thermostat setting, the central heating has ceased to function.

I've replaced the the circulating pump with exactly the the same model: Grundfos UPS 150-50 and replaced the Mid position 3 way valve [Drayton/Invensys] MA1/679-3. And still no central heating.

As long as the hot water is on - and the boiler is in a heating cycle - switching the cental heating on at the same time will heat the radiators too (as I would expect).

The thermostat, pump are all working fine, the acl programmer switches on and off ok, and the boiler works fine on the hot water cycle. (I've even tried two different room thermostats too with no difference. (I've also made sure that there's been no real changes to the system just direct replacement of parts.) The radiators have been bled to death, I'm certain there's no airlocks anywhere in the system and the header/expansion tanks are OK too.

I'm a bit stuck for ideas as to what might be wrong now: ideas anyone - it's getting a bit chilly now ?

Thanks for any posts/ advice offered!

 

[cross thread]

might be a faulty cylinder stat not switching the d/valve to heating only after h/water is satisfied,

 

[gas4you]

Certainly sounds like a 3 port valve problem. What make is it?

Are you sure you have wired it in correctly?

Could be the cyl stat, but you really need to test circuits with a multimeter before changing parts like there is no tomorrow.

 

[leehin]

I definitely wired it back in correctly: digital camera pics of the wiring to prove it! The pump and valve were definitely cream crackered. Pump doesn't work if I wire up to supply and the less said about the motor in the 3-port the better.

I'll get the multimeter out and check the other bits: I never thought of checking the cylinder stat.

Thanks[/i]