Motorized valve stuck in open position.

[a4007035]

Hi
We have 2 thermostats for our house. One for upstairs and one for downstairs.


When the downstairs thermostat is turned all the way down, the radiators still come on and get hot.


I checked the motorized valve and the lever on the side has no resistance whatsoever. I think this means it's permanently stuck in the open position. The valve is a Sunvic valve.

 

[CountryFan]

Yes, seems logical. Probably struggle to get a replacement powerhead (likely failed component) but a quick search suggests some brands are interchangeable with Sunvic. Looking at the screws, I would say the head is removable and the spindle could then be checked.

 

[ericmark]

I checked the motorized valve and the lever on the side has no resistance whatsoever. I think this means it's permanently stuck in the open position. The valve is a Sunvic valve.

Is this with the power to central heating turned off? If so motorised valve faulty, if not, it may be powered so valve not faulty.

 

[a4007035]

Yes that's right.
When the boiler is off, and the thermostat is turned up the light on the zone valve is on. When thermostat turned down, light goes off.
However, when the boiler is on the heating is always on regardless of what position the thermostat is on. There is a lever on the side of the valve to switch from auto to manual. But it has no give at all. We have a second zone valve and that is fully working and there is resistance if you try to switch the lever from auto to manual.

 

[Madrab]

When the downstairs thermostat is turned all the way down, the radiators still come on and get hot.

To clarify, the downstairs stat isn't calling for heat but the upstairs stat is, so the boiler is on? When that's the case and the downstairs stat isn't calling for heat and the valve's light is off the downstairs rads will still heat up?

If so, when you turn off both of the stats and the boiler then shuts down, is the downstairs valve's manual lever still loose?

If so, then if you want to test the motor then you want to take the actuator head off the valve - 2 screws - and see if you can turn the spindle of the valve, it should move very easily. Once that's checked, with the head off the valve, turn on the downstairs stat and see if the motor starts and the centre spindle of the actuator moves, if it does, then turn it off and see if the valve returns to the where it started.

 

[Harry Bloomfield]

If so, then if you want to test the motor then you want to take the actuator head off the valve - 2 screws - and see if you can turn the spindle of the valve, it should move very easily. Once that's checked, with the head off the valve, turn on the downstairs stat and see if the motor starts and the centre spindle of the actuator moves, if it does, then turn it off and see if the valve returns to the where it started.

If it fails that test, then a replacement actuator head, is available here and several more places. Shop around...

Sunvic / Danfoss 22mm 2 Port Actuator Only (White Head) HPA2

Sunvic 22mm 2 Port Actuator Only (White Head) - No longer available ** REPLACED BY DANFOSS ACTUATOR ** Note this is a DANFOSS Actuator (HPA2) ** The Danfoss actuator will replace the Sunvic SZ1301 model (Complete with Indicator Light) ** Note brass body is not included - White Actuator Head Only...

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