System as is follows:
- 17 radiators of various sizes - approx half upstairs, half downstairs.
- 1 year old boiler - Worcester Bosch Greenstar 34CDi Classic (a combi)
Problem is that 2 radiators upstairs are cold...
When the boiler was installed I had them both replaced, single panel for
a double inc replacing the TRVs, as they had always been much colder
than the rest.
Both seem to work fine initially, but over the last year have gradually
started to get colder and colder (when the system is on) until they are
now totally cold.
Not a clue what is wrong, but these are the things I observed:
- Original system (inc. radiators) is plumbed using 15mm copper.
- We had an extension built several years ago, and several radiators
were added. For those, the pipes running into/from the new radiators
(i.e. last ~0.5m) are flexi 10mm pipes (the lazy bu**ers couldn't be
bothered with soldering straight joins...).
- In the case of the two cold radiators, the 10mm pipes attaching them
to the 15mm pipes are much longer - approx. final 2-3m.
- When system is on. the feed into one of the cold radiators is warmish,
outlet is cold. For the other radiator both pipes are cold.
Any idea what is going on here?
On Wed, 26 Feb 2014 05:52:24 -0800 (PST), Jonathan wrote:
Even if virtually full of gas there still ought to be flow through
the bottom, so the pipes should be hot even if the majority of the
radiator is cold.
I'd go for a "blockage". This could be stuck TRV's (common),
disintegrated washer in a valve or possibly a build up of crud in the
I'd start with bleeding, if that doesn't help move to the TRVs and
make sure they are open with the control heads off if that doesn't
help move to excercising all the valves to fully open first then off
repeat a few times and retrun to the orginal setting, this with the
Agreed. And *when* you bleed, do each side of each rad separately - i.e.
bleed with one valve open and one closed, and then the other way round.
That way, you'll make sure that both pipes are bled and - in the event
that no water comes out of the bleed valve - you'll know which side the
It sounds like the system has never been properly balanced. It could
simply be a case that the new rads just don't get any flow since the
rest of the system poses a much lower flow resistance.
Have a read of:
It might simply be trapped air (worth checking) or it might be stuck
TRV valve actuator pins. You can check this quite easily by removing
the TRV heads to reveal the actuator pin which should be in the fully
You can easily check this by using a pair of pliars to push the pins
down and check whether or not they will return back to fully raised
immediately the down force is removed.
They may only move a millimetre or so before 'bottoming' which is
indicative of a sticking actuator pin in which case those pliars come
into their own for pulling the pin to the raised position (but don't
get too carried away with the applied lifting force!).
If this is the case, they usually free off after a few cycles of push
pull activity and you should find the radiators will warm up quite
rapidly unless, of course, they are in need of bleeding as well (not
uncommon with top floor radiators).
I once experienced a similar problem with our top floor radiators
after refilling this gravity pressurised system due to air locks in
the floor distribution manifolds which, afaicr, required me to set the
pump to its max setting and shut all the other rads off using their
TVR valves to force the trapped air 'round the bend' and into the top
floor rads where it could then be bled from the system.
I think I left it running this way for 20 or 30 minute periods
between each bleeding attempt before there was no more sign of air
accumulation. Once the system had been fully primed, I opened the TRVs
on the other rads and knocked the pump speed down a notch.
Now it's just a matter of checking for air in the top floor rads by
the expedient of checking that they're equally hot from top to bottom.
Opening the bleed valve as necesary is all that is required. Since I
can't recall the last time I had to bleed these rads, trapped air is
not a problem.
- Closed all the radiators apart from the two offending ones.
- Turned boiler on.
- Waited until the started to warm up, and bled them both. One had no
sign of air, but the other (that was always completely cold) let out
some air (with water) from one of the panels.
- Opened all the other radiators around the house, and so far at least,
everything works fine, including the two radiators that have been all
but dead for the best part of a year.
Many thanks for all the very useful advice - much appreciated! ... and I
definitely learnt a thing or two.
PS: Will check to make sure the pressure is still OK once the radiators
Was celebrating too early... :-(
Checked the pressure of the system once the radiators were cold, and it
was still OK.
However, tried to run the heating for a little while again to
double-check that the two radiators were still working (still couldn't
believe that they came back to life after such a long while...), and
they are already noticeably colder than all the others. If I remember
correctly, then this is how they gradually stopped heating up last year.
What does the learned panel think? Time to try to balance the system
next? I already ordered an IR thermometer - looks like a nice toy if
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