No heat to radiators, Hot water fine - Altherma SpaceAir

20 Oct 2010
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United Kingdom
Have an Altherma SpaceAir heating/hot water system. Just tried the central heating for the first time in months, but the radiators do not heat up, no matter how high I make the temperature.

Compressor and heat pump both turn on when the heating is switched on, however no hot water reaches the radiators. The sanitary hot water tank works fine, so I know the boiler (heat-pump) is working.

Had a look at the unit in the loft - the pipe that runs from the Actuator (Siemens DVA3) to the hot water tank is warm to touch, however the pipe that feeds the radiators is only warm next to the actuator, then become cold after about 10cm. Switching the actuator from Auto to Manual does nothing.

Any suggestions what I need to do/replace would be much appreciated.
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Doesn't feel like the switch is doing anything - moves very easily.

Should I remove the cover of the actuator to get a better idea?
Yes, it sounds like the body of the valve is stuck in one position. Remove the head, a quick spray of WD40 around the spindle and see if you can get it to move - gently at first, backwards and forwards. Also while it is off have a look at the head - turn the heating on and off and see if the actuator itself is moving.
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Thanks plumbersmate1! Took the head off, something unclicked, put the head back on and now the manual-auto switch actually works. Heating comes through on the auto setting.
I didn't spray any WD40 on, as it came free straight away. Would you recommend spraying some in there anyway?

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