Radiators hot when hot water on

[NickDu]

My rads throughout the house are blisteringly hot when hot water is on, and keep going regardless of thermostat temp; when hot water is off they do not heat, even when heating is set to on and thermostat up high; I have 2 x 2-way motorised valves in the airing cupboard, both replaced in 2019.. Have taken the motors off, applied WD40 to the metal notch coming out of the valve and twisted each with fingers to make sure they're free (which they are). Do I need to replace one or both motors (in which case which one?), which I can do - or the whole valve - which I'm not capable of doing? - thanks in advance, any advice gratefully received

 

[Deleted member 120897]

I take it this hasn’t always happened? Sounds like one of the valves is passing, likely the heating one when hot water calling.

 

[NickDu]

I take it this hasn’t always happened? Sounds like one of the valves is passing, likely the heating one when hot water calling.

Hey Chris - thanks for reply. No, started 48 hours ago. Been tropical in the house ever since! Did have the same problem about 7 or 8 years ago, plumber replaced the powerhead only, on one of the valves

 

[Deleted member 120897]

Staring from cold, put the hot water on, leave it say 10 minutes and feel the heating pipe the closed side of the 2 port, if this is warm or hot, you have a valve letting by.

 

[NickDu]

Staring from cold, put the hot water on, leave it say 10 minutes and feel the heating pipe the closed side of the 2 port, if this is warm or hot, you have a valve letting by.

I'll give it a try - thanks for the advice. I'm guessing if this is the case then the whole valve needs replacing? My big challenge is - I don't know which is the heating pipe...judging by the direction of the arrows on the valves, one IS feeding into the 'primary flow' at the bottom of my heatrae sadia megaflow tank, the other seems to be feeding FROM the 'primary return' halfway up the tank - I say 'seems' as the pipework around that valve is like spaghetti junction

 

[Deleted member 120897]

If you’re unsure, post a photo, but sounds like you sussed it.

 

[Basher]

If rads only heat when HW on, and do not heat when only Rads on, then boiler cannot be getting its power from the Rad 2-port valve (orange wire). The Rad 2-port must be physically open if they're getting hot, but maybe the motor is not managing to drive to the end of travel and operate the microswitch. (incidentally on some valves the manual lever does not move far enough to operate the microswitch either)
I would try replacing just the head on the valve you decide is on the rad. circuit !

PS Have you tried running the system with the head off the Rad 2-port, to see if it kicks into life. Just wondered if the 2-port is stopping the head from being able to travel fully to microswitch?

 

[NickDu]

If rads only heat when HW on, and do not heat when only Rads on, then boiler cannot be getting its power from the Rad 2-port valve (orange wire). The Rad 2-port must be physically open if they're getting hot, but maybe the motor is not managing to drive to the end of travel and operate the microswitch. (incidentally on some valves the manual lever does not move far enough to operate the microswitch either)
I would try replacing just the head on the valve you decide is on the rad. circuit !

PS Have you tried running the system with the head off the Rad 2-port, to see if it kicks into life. Just wondered if the 2-port is stopping the head from being able to travel fully to microswitch?
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Quick update - all working! Thanks for all the advice. Motor switched and all good