Hot water okay but scalding hot when CH is on

[evilcrafknife]

Hi all you experts out there

I hope someone can help me. My hot water seems to be hot-ish when my central heating is off but scalding hot when the central heating is on. This is a little bit annoying as I dont have mixer taps. Any ideas?

Also, one of my upstairs radiators only gets lukewarm but the pipe is very hot at the valve though. I'm assuming that it's a problem with the thermostatic valve. I took off the cap on the valve, but the pin seems to be moving freely. Do I need to replace the valve?

Thanks in advance for any replies.

Ta!

Kev

 

[sotal]

Sounds the same as mine:

//www.diynot.com/forums/viewtopic.php?t=207452

 

[namsag]

Motorised valve is passing and getting up to temp boiler stat is set too.

Even though pin moves, seating maybe stuck try gently tapping pin a few times or valve body AFTER making sure opposite side valve is open and turning a few other rads off to try and force any possible airlock in pipes out the way

 

[evilcrafknife]

Thanks for all of your help. Turning off the other radiators seems to have fixed the cold radiator.

I still have the problem with the scalding hot water when the central heating is on though. Namsag, I don't quite understand the meaning of "Motorised valve is passing and getting up to temp boiler stat is set too."

Any more ideas?

 

[namsag]

Do you have 2 two port valve or 1 mid position valve.
Basically when your cylinder is hot enough the cylinder stat cuts power to the valve and the valve closes sealing the exit port but these wear and can still allow water to pass if heating is being demanded .
The boiler stat can allow the system water to get up to around 90 degree`s cylinder is usually set for 60 so even though stat is satisfied and (worn) valve has closed you still have very hot water passing through the valve heating the cylinder way above what it should be

 

[mikely]

If you have a gravity-fed hot water system (likely to be no tank thermostat or motorised valves), then the water will be hotter when the heating is running a lot. The water temperature is only controlled by the boiler thermostat so you can turn the boiler thermostat down, but this will also reduce the radiator temperature.

The cold radiator may be due to poor balancing of the radiator system (See FAQ 5 in the WHICH Boiler and Central Heating FAQs).