Motorised Valve Always Open

I have a central heating and hot water system that was installed a couple of years ago, and works, providing heating and hot water as it should . That should be the end of the story, but the loft space ( 10 cubic metres) that the Worcester boiler and the pressurised hot water cylinder are installed in, is very warm, to the extent that it overheats the adjacent room quite considerably. It has always been hot as far as I remember. Today I did a bit of investigation.

The flow and return pipes to the boiler are constantly hot, even without heating being on, and when no hot water has been used for some time. The motorised valve controlling flow of hot water to the pressurised cylinder is always open, ie the lever is loose, and the pipes both sides of the valve are hot. Every ten minutes or so the boilers internal pump starts for a few minutes, but without heating. It appears from the boiler display that the pump action reduces the water temperature of the boiler and then switches off. Full disclosure, the boiler thermostat ( which controls both heating and hot water) was set to about 70 and I have reduced it to the 'eco' setting of 55, which may account for why the cylinder water temperature is higher than the boiler wants it . However before I reset the temperature, the motorised valve was still open and all the pipework was hot.

So I surmise that because the hot water motorised valve is open all the time that hot water from the cylinder is free to flow through the pipework to and from the boiler.

Any ideas why this valve would be always open, without the boiler firing up for heating. Or any other diagnosis I could check for. ?

Photos of your setup including all motorised valves, programmer and pipework between boiler and cylinder would help.

If the valve is always open, as in constantly firing up the boiler to heat, the microswitch is probably jammed open sending a constant live feed to act as a “call” for hot water.

Most likely the synchron motor has seized in the open position

ianmcd said:

Most likely the synchron motor has seized in the open position

Click to expand...

I agree, assuming the system did once work properly.

Thanks all - just to clarify, although the valve is clearly open the boiler is not constantly heating. Presumably it does heat when the cylinder thermostat calls for it, as the system produces hot water. I suppose my first question is whether the valve being open in such a situation is an issue or not.
I am not sure whether it has always been this way - certainly the air temperature in the loft space has been high for a long time, possibly since the system went in - but I dont know what the status of the valve has been over that time.
Is it possible that it is has been wired in wrong since installation ? What else could cause it to stay open but not call for heat. ?

thanks

Turn the sused spur for the heating off, if the valve now closes it is a control problem somewhere, if it stays open then the valve synchron motor has seized unles it is a MOMO valve of course as you have already beed asked a pic tells a lot more than you are telling us

When the need for heat to the cylinder is satisfied (thermostat) or the time clock is outside the HW on hours, the valve should be closed. If not, then whenever the CH is on, it will be trying to heat the cylinder too.

Does the valve close, when the whole system is powered off - judging by your mention of it having a lever, it is a spring return type?

Thanks again guys
IanMcD - turning off power to heating system caused the valve to close. So as you suspect, a control problem rather than a seized motor ?
Harry B - it is a spring return valve. Photos attached. But as Ian asked too, the valve does close when the power to the whole system is turned off.

Could this be a faulty cylinder thermostat -constantly calling for heat and forcing the valve to stay open ? It is fitted into an air pocket into the cylinder held in place by a single grub screw - never looks particularly solid design to me. Is there a way to verify the operation of the thermostat ?

Also, regarding it being a a control problem - let me check my understanding. When the time clock is inside the HW-ON hours, the valve should still be closed if the heat to the cylinder is satisfied - correct ?

If it is the case that it should be closed even during HW-ON, and you dont believe it could be a cylinder thermostat issue, then I will have to get someone in to verify the installation - there is plenty of scope for this not having being done properly in the first place, which I could elaborate on, but I fear it would complicate the question I am asking.

Thanks

BobbyOllox said:

Could this be a faulty cylinder thermostat -constantly calling for heat and forcing the valve to stay open ? It is fitted into an air pocket into the cylinder held in place by a single grub screw - never looks particularly solid design to me. Is there a way to verify the operation of the thermostat ?

Click to expand...

If it is a mechanical thermostat (click, click type), rather than a sensor, adjusting the temperature up and down should cause it to click open and closed at around the temperature of the cylinder. Doing so, should also operate the valve if it is in an active on a time basis. Disconnecting and insulating the wires, should also cause the valve to close, but do that with the power off.

When you switch the HW on at the programmer it sends power to the Cyl stat, if the stat is calling for heat, it sends power to the zone valve to open, which in turn brings on the pump and boiler, when the Cyl stat is satisfied it closes the valve , which in turn stope the boiler and pump (unless CH is on, but with the valve closed it will stop heating the Cyl) if the programmer HW is switched off the valve will close and the Cyl stat does nothing ,so if the valve is powering open with no demand for HW, there isnt a fault with the Cyl stat, then it is not wired correctly

Thank you guys - it is the cylinder thermostat that is kaput. The boiler is filling the cylinder with water at about 60 degrees. I had to turn the cylinder thermostat down to about 30 degrees before it shut down the motorised valve and turned the boiler off. I then had to turn it back up to about 45 degrees before it turned it back on. It had been set to about 55 degrees, so would have needed water temperature of about 85 degrees to trip the thermostat. I guess that it should be switching on and off a couple of degrees either side of the set temperature - and needs replacing. Thanks for your advice - beers on me when your passing.....

Careful, I think that Megabus is still going

rhinosaw said:

Careful, I think that Megabus is still going

Click to expand...

Megabus ???

OP - Once you have installed the new stat, you will need to set the cylinder stat several degrees lower than the boiler's output temperature so as to make it switch the demand for more heat to the cylinder off.

When you get a new Cyl stat you need to set it around 60 C, and the boiler thermostat has to be set higher than that, this is to prevent legionella forming inside the Cyl