Loud grinding noise followed by no central heating


8 Sep 2020
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United Kingdom
Hi All

Have run into an issue with heating at not the best time of the year. A few nights ago at 2am, a loud grinding/buzzing type sound was coming from the cabinet where the water tank, central heating pump and motorised valve etc are located.

This noise eventually went away however the next morning i found the central heating would not work. The (wireless) thermostat downstairs is fine, the receiver for it (located upstairs) is also fine. There is a LED light lit green on the receiver showing the heating is on but the all the radiators are completely cold.

Having spoken to a tech, suspicions are pointing to the central heating pump being faulty. There is no noise coming from the pump at all, it is completely silent, even when the lever on the pump is switched between the 3 settings.

The pump is a Grundfos UPS 15-50. The pump is hot when touched, not scorching but quite warm but as i say, no noise coming from it and the fact that loud noises where heard before the heating went down is what leads us to believe it may be that.

Just curious if anyone else has any thoughts.

Note, the heating has been working fine for many years now, whatever has happened is suddenly, no changes were made or tinkered with prior to it.

Let me know if you need anymore details. Thank you.
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Sounds like it could be the pump, or the motorised valve (as this turns on the pump and boiler).
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Reactions: V0Y
Thanks Chris

So i can hear a light buzzing sound coming from the motorised valve. A sounds that's always been there. I also pushed the small lever on the valve and it had a spring like effect so sprang back to pretty much half way point. When i pushed the lever, the valve went quiet and then a few seconds later the buzzing sound began to build up again. Note, if the cabinet door is closed you can barely hear the buzzing from the valve.

Hot water works fine, only the radiators are not heating up.
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Hot water works fine, only the radiators are not heating up
That's a key comment. I take it you have a hot water cylinder and just the one motorised valve?

If you are getting hot water then the pump should be working otherwise you wouldn't have hot water. When the system is calling for heat
(HW+CH), does the pipe to and from the pump get hot and then the pipe to the motorised valve and then the pipe out to the hot water cylinder warms up?

If they do then move the motorised valve's manual lever over to the other side and lock it in place, do both pipes from the valves then warm up and you start to get CH?
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Reactions: CBW
Opted to get a local plumber in, diagnosed as the valve head being at fault.

Thanks all, good to understand these things a little to at least do basic troubleshooting.

Last thing i wanted was to call out a plumber to replace a set of AA batteries :D

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