Problem after splitting a radiator

[WanderOverYonder]

So about a year ago we moved in to the current house and in the living room was a large single radiator (600 x 2400) that dominated the wall and was not really working well.
I decided to split this out in to two 600 x 800 double panel units and did this using an equal tee on both the feed and return for each unit.
All was well until about a month ago, the second unit (farthest away) is now not heating up like the first one. The feed pipe is very hot but the unit itself is only warm.
What could cause this to start happening?

Many thanks

 

[motorbiking]

If the feed pipe is hot, then its either:
- trv fault/closed
- return fault/closed
- air in the radiator
- blockage in the radiator

Bleed it.
remove the trv head and push the pin up and down
check the return

if all else fails remove rad and blow through with a hose pipe.

My guess is its air

 

[jackthom]

Are thermostatic valves fitted to the radiators. The one on the cool radiator may be stuck in the closed position.
In any case make sure both valves are fully open and try restricting the flow through the good radiator as this may be the easiest path for the circulating water to take.
Did the old single big radiator get nice and hot? Your original problem may have been insufficient flow in that part of the system, something which changing the number of radiators would not address.

 

[WanderOverYonder]

Thanks chaps, the old rad was hot but not toasting hot.
It is TRVs on both (Danfoss RAS2) and just tested closin. The valve to the good rad, the second one does heat up. I have bled it several times and it's just water coming out.
Would it heat up with the flow restricted to the good rad if the TRV was stuck?
It's odd as this has worked for about 11 months then just seemed to stop.

 

[jackthom]

It's common for trvs to stick in the closed position after being left that way over the summer months.
If it's stuck you'll get little or no flow whatever else you try.
Remove the trv head and see if the pin is up and if it can be pushed downwards with a suitable tool. It has a strong spring and should pop back up when released.
If it's stuck down try a few gentle taps sideways and push it downwards a few times to free it up, but don't force it up with pliers.

 

[WanderOverYonder]

If it's stuck though, would that not stop it heating up when I close the valve to the first rad?
It seems to work fine when it's just working on its own but open the valve on the first rad again and it cools down.
It's doing my nut in.

 

[jackthom]

If the valve was stuck but part open it would usually free up once it had been completely screwed down and opened up a few times so I'd try doing that at least. Has the heating worked properly this season and just suddenly started playing up?

 

[WanderOverYonder]

If the valve was stuck but part open it would usually free up once it had been completely screwed down and opened up a few times so I'd try doing that at least. Has the heating worked properly this season and just suddenly started playing up?

Heating has worked ok for 11 months, just this last month it's been funky. It's the only rad in the whole house that doesn't heat up. I have just put cleaner in to the system as a precautionary measure but doubt it's dirt causing it as its just that one unit.
It's just odd that once the first unit is shut off the second one works fine.

 

[jackthom]

The water is just taking the path of least resistance through the good radiator. All you can do is make certain both of the valves on the cool one are completely open. Then if there's still an imbalance, partially close the lock shield valve on the hot radiator to try and balance the flow between the two radiators.
Are these radiators supplied by 15mm pipework and do you know if that is a long run or maybe even shared with other radiators elsewhere in the house.

 

[WanderOverYonder]

The water is just taking the path of least resistance through the good radiator. All you can do is make certain both of the valves on the cool one are completely open. Then if there's still an imbalance, partially close the lock shield valve on the hot radiator to try and balance the flow between the two radiators.
Are these radiators supplied by 15mm pipework and do you know if that is a long run or maybe even shared with other radiators elsewhere in the house.

It's micro bore throughout the house, not a particularly large house in terms of floor area so wouldn't think long runs. I don't know about the distribution between other rads though.
Thanks for the balancing suggestion, will give it a go.

 

[WanderOverYonder]

Ok, so the TRV pin seems to move freely without sticking.
I also closed the lockshield on the good radiator (save 1/4 turn open) but no joy.
As the living room already has a TRV controlled rad that works, would replacing the TRV on the second rad to a normal valve make a difference do you think?

Cheers

 

[jackthom]

TBH It's pushing things a bit running two large radiators from one long microbore feed, especially if the pipework is getting old and becoming clogged. Ideally you could look at running some new pipework from the manifold ( or the point where the microbore starts ). Either 15mm to supply both radiators or an additional 10mm run just for the second one.
I know that's easier said than done depending on the type of flooring etc.

 

[WanderOverYonder]

TBH It's pushing things a bit running two large radiators from one long microbore feed, especially if the pipework is getting old and becoming clogged. Ideally you could look at running some new pipework from the manifold ( or the point where the microbore starts ). Either 15mm to supply both radiators or an additional 10mm run just for the second one.
I know that's easier said than done depending on the type of flooring etc.

Not much chance of that in the short term I'm afraid so ideally looking at a reasonably quick (if temporary into summer next year) fix.
The feed pipe into the second rad is burning hot but none of it seems to be getting in to the rad itself, hence me asking if a normal wheel valve would possibly help.

Thanks for the suggestion though, defo something that we will look at next year when extension work starts.

 

[jackthom]

Is the system open vented with a header tank? In which case it makes the old bucket test easier. This involves emptying only the radiator with it's valves turned off then disconnecting each valve in turn from the radiator.
With something like a bucket to catch the water, turn on the disconnected valve to get a good jet of water flowing through the valve into the bucket.
A good strong flow of water would indicate the pipe and the valve aren't blocked, plus it can help clear out some sludge if it's partially choking the pipework.