Honeywell 3-way motorised valve - draining the system query

[Skylark NW]

I have a conventional hot water and central heating system, installed in 1987 when the house was built.

The radiators appear hotter than the thermostat would suggest. There is no response to turning the thermostat down. The thermostat, mounted in the hall, clicks on and off when rotated, as normal.

Several years ago, with much appreciated help from this forum, I replaced the motorised valve head only. I'm now thinking that the valve is sticking and it's to replace the body with a complete new unit.

I've read that the system needs to be drained. Does this generally mean the central heating system only or does it also mean the hot water tank?

Many thanks in advance for your help.

 

[CBW]

The room thermostat doesn’t have any affect on the water in the radiators, this is done by the boiler thermostat.

 

[cross thread]

Just the system ,is it not valved off ,most are

 

[Skylark NW]

The room thermostat doesn’t have any affect on the water in the radiators, thief is done by the boiler thermostat.

Thanks, Chris,
Not sure that I fully understand the role of the room thermostat. I've since "worked" the motorised valve around 20 times and radiator temperature now appears to be responding to room thermostat position once more. The water tank thermostat is the originally fitted ACL HTS2. It is set fully counterclockwise, min, but hot water temp is good. It's been in this position for years and I'd simply assumed poor calibration.
I'm tempted to change the motorised valve and install an HTS3.........but the pressure to act quickly has eased.
Appreciate your views.

 

[Skylark NW]

Just the system ,is it not valved off ,most are

Thank you. Only one port, pump, is valved, the other two are not.

 

[dilalio]

Thanks, Chris,
Not sure that I fully understand the role of the room thermostat. I've since "worked" the motorised valve around 20 times and radiator temperature now appears to be responding to room thermostat position once more. The water tank thermostat is the originally fitted ACL HTS2. It is set fully counterclockwise, min, but hot water temp is good. It's been in this position for years and I'd simply assumed poor calibration.
I'm tempted to change the motorised valve and install an HTS3.........but the pressure to act quickly has eased.
Appreciate your views.

The roomstat measures the air around it and opens/closes a contact accordingly.
Boiler thermostat measures the temperature of the water flowing through the boiler and opens/closes a contact accordingly.
If your boiler stat is set to 70° then the water flowing out to the rads will be 70° (unless modulating boiler) regardless of what your roomstat is set to.

 

[fixitflav]

If your boiler stat is set to 70° then the water flowing out to the rads will be 70°

Unless the weather is not too cold, in which case the roomstat can be satisfied before the boiler flow reaches control-stat setting.

 

[dilalio]

Unless the weather is not too cold, in which case the roomstat can be satisfied before the boiler flow reaches control-stat setting.

My point was to explain simple concept to OP.
Boiler can still get water temp to 70 before roomstat detects rise... There's a myriad of scenarios, no need to explore them all here and now.

 

[fixitflav]

My point was to explain simple concept to OP.
Boiler can still get water temp to 70 before roomstat detects rise... There's a myriad of scenarios, no need to explore them all here and now.

OK no problem, just thought I'd mention it

 

[Skylark NW]

The roomstat measures the air around it and opens/closes a contact accordingly.
Boiler thermostat measures the temperature of the water flowing through the boiler and opens/closes a contact accordingly.
If your boiler stat is set to 70° then the water flowing out to the rads will be 70° (unless modulating boiler) regardless of what your roomstat is set to.

That's helpful, thank you. So, the roomstat is feeling chilly so it sends a signal to circulate water around the system. Separately, the water temp is measured and controlled by the boilerstat. As soon as the roomstat has warmed, it sends another signal to stop circulating the water. Now it makes sense and helps diagnose my problem. The hot water was being circulated despite the roomstat telling it not to. Hence sticking motorised valve. Really appreciate all of you taking the time to respond.