CH valve actuator problem?

We've just moved into a new house and was going to get the boiler serviced, but discovered the central heating wouldn't fire up.

The upstairs and downstairs heating is controlled seperately by seperate timers - downstairs timer also controls hot water.

Hot water works fine on timer, and upstairs central heating works fine when called.

The downstairs heating though doesn't seem to want to work when called without the hot water on.

There are three seperate motorized valves with actuators on them (Siemens DVA 2/5?). One each for upstairs, downstairs and the water.

With the heating/hot water off on the timer (or at least not calling), I took the actuators off the valves for the downstairs heating and then upstairs heating.

There's a lever on the side to go from auto to manual. When I moved the lever on the D/S actuator, nothing happened (and don't know if I was expecting it to!). When I moved the lever on the U/S actuator the pump started and the boiler kicked in...

Have we got a duff actuator on the downstairs heating circuit? (I originally took the heads off to make sure that the valves were moving freely, and they are).

The last owner told me that they played around with the lever last winter and it all started working....

Any help/ideas really appreciated.

Cheers.

It could be a failed Synchron motor in the CH valve.

Have you checked your room thermostat, weather compensation etc? It is high summer, and your controls could simply be holding the heating off.

I have been called out more than once to a problem like this, only to find the room 'stat turned down.

Mysteryman,

Thanks for the answer. Yes, room stat was up full - clicked on etc.

Some more info from playing around this weekend. I put the heating on timer with the hot water (room stat on full) so they both came on together.... and hey presto, hot radiators.... if I turned the room stat down, radiators cooled down, and came on again if I turned it back up again.

So, once the hot water/CH had switched off on the timer, I tried turning the CH on again on its own (didn't touch anything else).... nothing. Boiler doesn't fire....

Does that point back to a dodgy actuator? Anything else I can test?

Cheers.

Check the wiring on the actuator to the affected circuit. Does that motor open the valve? If not, the boiler will only fire when another valve is also open and calling. The end switch on any valve does not switch on with the valve manually open. The three end switches must be wired in parallel - usually with the three grey wires to a permanent live and the three orange wires to power up the boiler and pump. Thus any open valve will boot up the boiler.

Mysteryman,

Wanted to come back and say 'Thanks' for the advice. Problem finally solved (after a lengthy process of elimination!)...

Checked over the wiring, and watched the actuator turn when the thermostat was turned on. So, we had power to the unit, but no signal to the boiler (which explained why we needed something else on to get heat downstairs).

As all the wires looked good (nothing obvious loose anywhere), I took the plunge and invested in a new actuator, as everything seemed to point to it as the problem...

Fitted it this afternoon, and all working! Boiler firing with downstairs thermostat!

Thanks again!

My daughter and husband recently bought a house that was built in 2010, the year that this thread started. Shortly after moving in, the Siemens actuator in one of the motorised valves malfunctioned, sticking open and calling for heat continuously, regardless of thermostat position.
The valve had been installed upside down.

I de-mounted the actuator and removed the cover it to check inside. There was a sticky substance on part of the mechanism. I cleaned this, lubricated, and put it back in place. It worked for about 12 hours then stalled again. On farther dismantling, the problems became apparent. Plastic parts interfacing with metal had worn and broken. Gear teeth no longer engaged, and the hinge pin of the main crank had sheared off.

My impression, this item has a design fault, poor choice of materials for mechanism.
How many have failed at 5 years of age?