I had a double radiator installed replacing a single rad, overall
dimensions were similar.A thermostatic valve was installed at the same
time. Whilst the new radiator gives out more heat than the old one it
only feels warm to touch when the others in the house feel hot.
Pipework is 10mm. Should the rad get hot or could the valve be faulty?
I've tried removing the controller but that makes no difference.
Any comments appreciated.
The double radiator has a lot more potential heat capacity than the single
it replaced - but that capacity can only be realised if the flow through it
is doubled. Assuming that the lockshield valve at the opposite end to the
TRV is fully open, you will need to rebalance the system - by turning down
the lockshields on some or all of the other rads, and maybe by increasing
the pump speed.
Just a final thought. Is the TRV direction sensitive, and perhaps fitted on
the return side rather than the flow side of the rad? That could be at least
part of the problem.
Make sure the non-thermostatic valve on the other end is only half open. If
you close it fully, turning it clockwise till it stops, then put a pencil
mark on the head, in line with one edge of the radiator. Now turn it fully
open, by turning it anti-clockwise, but count how many full turns it takes
to get it fully open by counting how many times the pencil mark passes the
same edge of the radiator that you marked in the beginning. If it takes,
for example, 6 full turns to open the valve fully, then turning it back in
only 3 full turns will mean it is as close to half way as you can get it.
Leave it like that for a couple of days to see if the radiator gets any
hotter. How this works, is by not allowing the hot water to escape from the
radiator as quickly as it is now, and this helps to retain the hot water in
the radiator longer and helps to heat it up more.
Sorry Mr Wallop, but you must have had too many Cods for tea!
Restricting the flow will make the rad *cooler* (what the hell do you think
that a TRV does?!) - in that the water in the rad will give up its heat to
the room at a faster rate than it is being replenished by fresh water.
The flow through this rad needs to be *increased* by restricting the flow
through other rads and/or increasing the pump speed.
What was the size of the radiator before, Peter, and what is it now?
How long are the runs of 10mm tube roughly?
As others have said, you can try balancing. However, there are
limits based on what the pipe will handle from the flow perspective,
so before you spend a lot of time doing balancing, it would be as well
to check whether everything is within reasonable range.
I'll give you an example. A neighbour with an 8mm system changed a
single panel radiator with an output of about 1kW for a large double
panel one with fins because he had built an extension. The new
radiator should have had an output of 4kW.
It never worked because 8mm tube of the lengths he had is nowhere
close to being able to handle the required water flow to support this
amount of output. Even if he turned off all other radiators and
opened the valves to this one fully, we measured and calculated that
he was getting no more than 2kW from it. The fix was to replace the
pipework in 15mm.
Hopefully you don't have this problem, but it would be as well to
check first. You could also do a simple practical test of closing
all other radiators and opening this one fully at both valves.
To email, substitute .nospam with .gl
Thanks for all replies and comments. I think that the first and last,
to date, poster have between them identified source of the problem.
I'll explain after answering Andy's request for more details.
The original radiator was 43in wide x 29in high; the new, double, one
is 43in wide x 23in high. It is located in the kitchen but also has to
heat the adjacent utility. I don't know the length of the pipe run
because the pipes are hidden in the wall.
The reason for upgrading the rad was because the ch boiler is in the
utility. Until just over a year ago the radiated output from the
boiler and rad just about coped. Then the boiler packed up and was
replaced with a Potterton Suprima 70, which I found radiates much less
heat into the utility, concluding that the original radiator couldn't
cope with the area concerned.
The valve controller is marked Bulldog 42 EN215. I don't know if this
is uni- or bi-directional, but ...
When I first put the heating on in the autumn I found that all of the
rad became warm except the area around the valve which remained cool.
As the heating was turned up the whole rad seemed to be the same
temperature and I thought that quirk had gone away. However I've just,
whilst typing this message, felt the radiator and found the valve cold
Your further thoughts/ideas appreciated.
Is the TRV on the flow or the return? If you're not sure, wait until the
system is next heating up from cold and feel the pipes. Obviously, the
hotter pipe is the flow. If the TRV is uni-directional *and* is on the
return . . .voila!
Was the old one single panel and with or without fins?
Is the new double one with fins and are they on both panels or one?
If you know the make and model of the new one it would help, but the
number of panels with fins would help so that the nominal output can
With respect to the pipes, do you think that they go up the wall? Is
the house a modern type, roughly square in shape? If so, what would
you estimate the horizontal distance to be from a point above the
radiator to the centre of the house? From this we could make a
reasonable guess at the pipe lengths, worst case, since they are
likely to connect to the main heating pipes at a manifold and centre
of the house would likely be the worst case location. I just want
to get an idea of whether the likely distance up the wall and across
is 5m or 15m or more.
That should tell us whether we are within range that can be balanced
or whether the amount of capacity now there in the new radiator is so
much that this is a no-hoper.
This does sound like an air lock may be the issue or that the TRV is
the wrong way round. Mainly they have an arrow on the base to show
the flow and the arrow is double ended if they are bidrectional.
If unidirectional and the wrong way round, they often rattle under
One thing that you could do is as suggested before, and close all
other radiators with their TRVs or wheel valves so that all the pump
effort goes through the new radiator. THat would probably clear any
airlock and would be another test as to whether you would be able to
fix this with balancing.
To email, substitute .nospam with .gl
OK. Given all of that, I looked up the closest Myson and Stelrad
radiators corresponding to your sizes and allowing for the boiler
operating at 80 degrees then the heat output of the old radiator would
be about 1450W and the new one about 2250W.
Assuming a 10m run of pipe in total, using the calculation method of
10mm pipe should still be OK. The new radiator needs a mass flow
rate of about 0.05kg/sec and 10mm tube will have a resistance of 0.1 m
head per metre run, i.e. 1m total. Assuming that nothing silly has
been done elsewhere, this should be balancable.
That should mean bidirectional.
It's sounding like an airlock or perhaps a blockage for some reason.
Was the water reasonably clean from the old radiator? Not too much
To email, substitute .nospam with .gl
From what I remember it was ok. I'll get on to the plumber who
installed it. I wanted to be sure if my expectations were reasonable
in case he tries to fob me off.
Many thanks for all contributions. I'll report back.
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