Central Heating problem.

[sunama]

Hi.

I have a problem with my central heating system.

I have an open vented system, (heating only) boiler, with a hot water tank.

I have a single, wall mounted thermostat in the hallway (for central heating).

I have a thermostat on the hot water cylinder itself (for hot water).

I have a 3 way motorised valve (Salus MV322).

My central heating has been working fine for 18 months or so.

Now today, I went to put on my central heating system and it didn't come on. Usually, I hear the pump fire up and some noise from the valve when the central heating comes on, but today, I heard nothing.

Nothing happens when the heating system is switched on. No noise. Nothing.

Now, the hot water is working fine. When it the hot water gets cold the boiler comes on as normal, as does the pump and the water is heated upto the desired temperature.

Test
I ran a test. While the hot water was heating, I switched the Salus MV322 valve to manual. A few minutes later, the radiators got hot (as normal). When the water heating was finished though, the pump stopped and the radiators went cold.

Could someone out there diagnose my problem?

 

[kevplumb]

actuator (motor) on the valve has gone by the sound of it

 

[sunama]

Is there anything I can do (before I fit a new one), to verify that it is indeed the motor that has broken?

 

[kevplumb]

turn the heating stat up and the tank stat down

the valve should motor

 

[sunama]

I tried that. Nothing happens.

 

[seco services]

use a multi meter on the wires to check for power to/from valve.

 

[sunama]

I don't have a multimeter, so will have to buy one.

Will this one be ok:
http://www.maplin.co.uk/Module.aspx?ModuleNo=37279&C

Or, I already have a "tester" which checks for live wires:

http://www.transtools.co.uk/store/p.../detectors/silverline-live-wire-detector.html

- could that be used instead?

 

[jackthom]

That tester should be OK.

Make sure the hot water tank thermostat is satisfied, turn it's temp dial right down if necessary.

With the room thermostat calling for heat the white wire and the grey wire to the valve should be Live and the valve should motor across to the CH only position.

A microswitch in the valve should then switch the orange wire to Live. This is what normally ignites the boiler and starts the pump for CH only.

 

[xr4x4]

Test
I ran a test. While the hot water was heating, I switched the Salus MV322 valve to manual. A few minutes later, the radiators got hot (as normal). When the water heating was finished though, the pump stopped and the radiators went cold.

Could someone out there diagnose my problem?

sounds like a control problem to me, after the hot water got to temp, nothing was calling for heat so the boiler switched off.

i bet if you kept the valve to manual, turned the hot water tank themostat up (only temp) i reckon the boiler will fire up and heat the rads up again untill hot water reaches temp.

what about the room stat, that ok? is it turned up? does it click when you turn it?

 

[seco services]

Test
I ran a test. While the hot water was heating, I switched the Salus MV322 valve to manual. A few minutes later, the radiators got hot (as normal). When the water heating was finished though, the pump stopped and the radiators went cold.

Could someone out there diagnose my problem?

sounds like a control problem to me, after the hot water got to temp, nothing was calling for heat so the boiler switched off.

i bet if you kept the valve to manual, turned the hot water tank themostat up (only temp) i reckon the boiler will fire up and heat the rads up again untill hot water reaches temp.

cause it will you've put the valve in mid position and using the hw to power the boiler.

the room stat will still click even if the mot valve has failed.

 

[sunama]

sounds like a control problem to me, after the hot water got to temp, nothing was calling for heat so the boiler switched off.

That sums it up.

i bet if you kept the valve to manual, turned the hot water tank themostat up (only temp) i reckon the boiler will fire up and heat the rads up again untill hot water reaches temp.

That is correct. While the hot water is heating up, with the valve motor on manual, the radiators also heat up. Once the hot water has reached its target temp, the boiler switches off (regardless of whether the central heating is on or not).

what about the room stat, that ok? is it turned up? does it click when you turn it?

Room stat clicks when I turn it, as normal.

 

[sunama]

One thing I didnt mention was that 18 months ago, I had a boiler engineer around. He fixed the boiler but stated that the valve motor was on its way out and suggested changing it. This was 18 months ago.

 

[seco services]

you need to check the wiring on the valve as we have said.
valves can go on for ages when they start playing up.

 

[sunama]

OK sure.

I don't have a multimeter, but I have this device:
http://www.transtools.co.uk/store/p.../detectors/silverline-live-wire-detector.html

Can that be used?

If not would this multimeter be OK:
http://www.maplin.co.uk/Module.aspx?ModuleNo=37279&C

 

[jackthom]

That tester should be OK.

Make sure the hot water tank thermostat is satisfied, turn it's temp dial right down if necessary.

With the room thermostat calling for heat the white wire and the grey wire to the valve should be Live and the valve should motor across to the CH only position.

A microswitch in the valve should then switch the orange wire to Live. This is what normally ignites the boiler and starts the pump for CH only.