Heating coming on when not timed to

[plumb_know]

Sorry for essay in advance,

Don't know if pics will be of help. customer mentioned that her heating was coming on during the day when it wasn't timed to and she has been recieving high bills. System was installed by bg 7 years ago, symptoms started as 1rad in hallway being hot all the time, engineer came out and turned trv down on rad but this just caused the bathroom rad to get hot instead. Customer just put up with this but now a year down the line all the heating is coming on even when it is not timed to and with the room stat turned right down.
The system is a s plan, the motorised valve seems to be working, I can see the arm moving and hear the motor working when turning heating on and off. The motorised valve for the hot water arm moves also when cylinder stat turned up and down, but the arm doesn't seem to move quite as much as the heating one. The heating return looks like it is teed in after hot water return. I am thinking that hot water is programmed to come on during the day and then isn't turning off fully once heated so the heat begins to circulate around the heating via the heating return where it is teed in after cylinder return?

But wouldn't this of happened from when it was first installed? Anyone know what could be causing this? I am going to go back to do a proper inspection, what should I be testing?
I don't have lots of heating experience but am self employed so the only way of me learning is by taking on new jobs and doing lots of research and hep from you guys.
Boiler is a baxi system 100he

thanks for any help

 

[doitmyself]

symptoms started as 1rad in hallway being hot all the time, engineer came out and turned trv down on rad but this just caused the bathroom rad to get hot instead.

"Engineer" is an idiot.

all the heating is coming on even when it is not timed to and with the room stat turned right down. The system is a s plan, the motorised valve seems to be working, I can see the arm moving and hear the motor working when turning heating on and off.

The motor may be working and the arm moving, but the CH valve could be sticking or letting by. Feel the pipe a foot or so after the valve to see if it gets hot when it shouldn't. Also, remove the actuator and check that the spindle can be turned easily by hand. A sticking spindle can usually be loosened by the application of a silicon lubricant. If pipe is hot and valve not sticking, it is letting by it is letting by. Complete new valve required. (If you have a Honeywell valve with removable actuator, you can get a repair kit Part No 272752A/U CARD.)

The heating return looks like it is teed in after hot water return. I am thinking that hot water is programmed to come on during the day and then isn't turning off fully once heated so the heat begins to circulate around the heating via the heating return where it is teed in after cylinder return?

If the heating return has been connected after the cylinder return then you will get reverse circulation. Definitely worth checking the connections are in the correct order.

 

[Chalked]

Passing motorised valve or dodgy wiring, the hot water could be back feeding the motor on the heating valve. To check this, turn hot water on only and make sure there is no power onto the brown wire on the heating valve. As for passing valve, turn hot water on and see if it gets hot after the motorised valve.
I would check both items.

 

[Anton]

If it was installed 7 years ago and it's only just started doing this now then it's the heating zone valve
the actuators on those valves in the photo are crap, and the valve body spindles stick. Change the full valve and head for a Honeywell.

 

[Ermintrude]

I concur ! The valves are pish. Swap both for Honeywell while it's drained. Easy way to check is remove ( orange I think) from either valve when no demand and check back to neutral for 240v if juice on s/l from valve means micro is dead. Valves will be passing and soon leaking on spindles no doubt. Check that cylinder stat works too.

 

[plumb_know]

Thanks everyone,

very helpful ful as usual, I will change both for Honeywell. Was thinking the valves looked a bit cheap.

will let you know if it worked.

thanks again