Pickling problem - help me out

Sparkpea

My sister was on the phone yesterday morning complaining her heating (gas open vented system) was making a "fog horn" sound around 3-4am the past 4 mornings and her hubby had to get up to flick a switch in the hot press which fixed it. The switch is the main switch for the CH.

Tbh she's complained about nosies in the hot press before and I had adjusted the bye-pass valve but the 'fog horn' sound seems like an exaggeration to me.

Anyway I went around last night for a look (wasn't great because no one was there to explain the sound!). So theres 2 zone valves in the HP. System has a sunvic timeclock, room stat, 2 sunvic zone valves and cylinder stat and a byepass. When the heating is turned on and the zone valve for the heating opens the head on the valve is making a humming noise and its vibrating through the pipes a bit. Yes you can hear it (its nothing like a fog horn) but it stops after 20-30seconds when the valve opens or closes.

I took the head off the valve and you can still hear the sound but its not vibrating through the pipework and there is also a sound of water running through the byepass (normal but a little louder because I think some air is circulating). Turns out someone had closed the dust cap on the AV on the flow at the HW tank. Pressure had dropped so I topped it up.

Ok next problem is why is this noise happening during the night? If its the motorised valve then yes it will be heard when the heating is on as the room stat will open/close the valve as required. My next thought was is there a faulty microswitch in the valve head thats bringing on the boiler/pump during the night (common enough fault). So I liked a wire between the 2, to act like the microswitch was faulty and the boiler fired and the pump came on (heard water running through the byepass) but the motorised valve did not come on/open/close so there wasn't the same humming noise.

Got pickled at this stage, theres a constant live going to the motorised valve and a constant live going to the boiler regardless whether the clock is on or off. I started thinking frost stat maybe? Its a mynute 20 e. Couldn't find a manual handy in her's so I googled.. couldn't find anything about a frost stat on the manual tho one alarming thing I did see was it said this boiler shouldn't be fitted on an open vented system?

So basically I'm wondering is there another reason as to why the motorised valve would open during the night when timeclock is off. I've suggested changing the head to eliminate the fact that there may be a faulty microswitch (tho it was all working when I was there) but I'm not convinced this is going to fix the overall problem - just eliminate 2/3 of the problems.

Jonny

Pete67

Have often seen heating controls (zone valves and room stats especially) wired from a different supply than the boiler. Wrong I know but common enough. So if the boiler is out on a timeswitch the thermostat can still be live and switch in the zone valve during the night.

Jedstaff

Could be a frost stat switching on boiler at night and just be a noisy bypass?