2 faulty motorised valves?

[Kevine]

Any developments? Interested to know how it went.

Sorry for late response. Got sidetracked... Since i had the heads off the motorised valves, i wanted to use immersion heater standalone to get hot water for the house, but since it's rarely used at the plug, it wasn't working. Turned out i needed a new rod thermostat so got that fixed.
In meantime as i had the heads off the motorised valves, they were making strange noises. As they were relatively cheap to replace, i replaced the motor heads.
Anyway, after all that, i still have the original problem. Rads getting hot when water on.
Testing further as suggested above, with the system cold and only firing the boiler up for water, it seems the rad valve is passing that heat..
I can only assume i have a bad valve, this was the last resort test as i was hoping not to drain the system.
But would you agree it is a valve problem and that should be replaced at the rad valve? or even both since i have the system drained?
Also, with system drained should i put some inhibitor or cleaner in the system.
I assume this must fix my problem, i hope!
Thanks

 

[fixitflav]

Testing further as suggested above, with the system cold and only firing the boiler up for water, it seems the rad valve is passing that heat..

In that case it sounds like a passing valve problem. Hopefully the pipework layout is correct, but still need to replace the rads valve. If both valves are many years old it could be worth changing both while you're at it.

Also, with system drained should i put some inhibitor or cleaner in the system.

Definitely! And if you haven't got a Magnaclean or similar worth adding one. Apart from its main job, it's very useful for sampling the water for a corrosion test, and topping up the inhibitor if required.