Reasons for lukewarm radiator?

[Pete321]

Hi all,

Looking for some advice on potential causes of lukewarm radiator. It's a bedroom radiator (double panel, single convector). When we moved into the house just over four years ago, it just didn't get warm. Took it off, flushed it, put it back on, not really any different. Changed it for a new one (mainly for cosmetic reasons) but always been the same:

• Generally cold to faintly warm along the bottom of the radiator (both panels).
• Warm, not hot, along the top.
• No air in the radiator.
• Inlet pipe is hot.

Installation:

• Original Danfoss TRV on inlet.
• Original lockshield valve on outlet.
• 10mm pipework.

Other points:

• Towel radiator in adjacent en-suite is nice and hot.
• Radiator directly below in lounge also hot.

Any thoughts on what causes a radiator to be warm along the top but cold along the bottom? Very low flow? Too high a flow? Somewhat blocked TRV or lockshield valve? Doesn't seem to make any different if the lockshield is wound fully open or a few turns open.

House is just coming up to 20 years old, on a housing estate. Can't think it has been like this since built but suppose it could have been. Don't really want to start pulling up the floor to look at the pipework but will if I have to...

Any suggestions greatly received!
Cheers,
Pete.

 

[centralheatking]

Hi all,

Looking for some advice on potential causes of lukewarm radiator. It's a bedroom radiator (double panel, single convector). When we moved into the house just over four years ago, it just didn't get warm. Took it off, flushed it, put it back on, not really any different. Changed it for a new one (mainly for cosmetic reasons) but always been the same:

• Generally cold to faintly warm along the bottom of the radiator (both panels).
• Warm, not hot, along the top.
• No air in the radiator.
• Inlet pipe is hot.

Installation:

• Original Danfoss TRV on inlet.
• Original lockshield valve on outlet.
• 10mm pipework.

Other points:

• Towel radiator in adjacent en-suite is nice and hot.
• Radiator directly below in lounge also hot.

Any thoughts on what causes a radiator to be warm along the top but cold along the bottom? Very low flow? Too high a flow? Somewhat blocked TRV or lockshield valve? Doesn't seem to make any different if the lockshield is wound fully open or a few turns open.

House is just coming up to 20 years old, on a housing estate. Can't think it has been like this since built but suppose it could have been. Don't really want to start pulling up the floor to look at the pipework but will if I have to...

Any suggestions greatly received!
Cheers,
Pete.

Faulty TRV jammed almost fully closed, take valve head off gently tap pin down to see if it pops up
Make sure locksheild fully open, replace trv valve body Centralheatking

 

[Pete321]

Faulty TRV jammed almost fully closed, take valve head off gently tap pin down to see if it pops up
Make sure locksheild fully open, replace trv valve body Centralheatking

Bingo! Thank you so much for that suggestion. Got a new Danfoss valve from Screwfix and swapped it over and now have a hot bedroom radiator for the first time since we’ve been here!

Here you can see the difference between how far the old pin is jammed in compared to the new one.

 

[Allgoode]

Also water - central heating is a lazy sod & if it can find an easy route to rtn to the boiler it will take it.
I would suggest as above first that the TRV pin needs to be free to move & then if you put some tape on the non TRV side of the lounge & en-suite rads and count the turns until closed and rtn to original setting.
I always change the TRV & L/S at same time as rad replacement or if issues change both of them at same time. (does not cost too much - EG - Danfoss RAS-C2 about £20).
Then over a day or two turn the flow on these down by say 1/4 turn at a time to see what effect this has on the other rad that only gets warm.
What you are doing in essence is performing a crude system balance which then makes the central heating water flow through the cooler rad.
You should be able to find an optimum balance by doing this.
Slightly time consuming but you can do it free of charge,
Hope this helps,
Andy

 

[Pete321]

Yep, bought the twin pack of TRV and L/S and pipe freeze, only when I got home did I realise the freeze can was only large enough to do one pipe

So got to get another to do the L/S 😞

Thanks for the balancing tips.

Pete.