I have just had a conservatory built. To allow this I had to remove an old radiator which was connected with 10mm microbore pipes and was working fine. After the conservatory was built I entended the pipes with 8mm pipe which I already had to the brand new radiator about 7m further away. However even though the feed pipe is red hot to the valve there is very slow flow through the rad so that the exit pipe is only slightly warm. I have checked for blockages in the feed and return pipes and there were none, and the situation improves only slightly when I turned off all the other rads in the house. Is the problem likely to be the smaller bore pipes or could there be another reason for this?
slow flow through new rad
- Thread starter spb
- Start date
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spb said:
What is the size of the radiator? A pump might have trouble servicing a
big radiator through 8mm pipe, especially 14 metres of it (7 metres there
and 7 metres back).
Presumably both radiator valves are fully open.
But every other radiator in the house is as hot as ever and all heat up pretty rapidly when the system is turned on, which I would have thought would be signs of a healthy pump. I have a feeling the problem is my fault for being a skinflint and not buying 10mm pipe just because I already had some 8mm. However I dont want to go through the hassle of changing it all if that isn't going to help.
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it is big - a double 1600mm x 600mm.
and yes both valves are fully open
I've never fitted a pump before. Is it something a DIYer can do with only basic plumbing skills. And what sort of cost are we looking at. Part of the pipework is under a suspended floor and only about 2m on top of a concrete floor. Would changing the small bore pipe to 15mm for under the suspended floor and using 10mm for the last run over the solid floor help?
spb said:
I am not a plumber but...
I'm currently in "discussion" with my housebuilder who used 12 metres of
10mm plastic to fit to a 400 x 1400 double radiator where the design
asked for 15mm pipe. My system will only balance with a temperature
drop of 15C and with lockshield valves on all other radiators virtually
closed (so some of them whistle as the water flows through them). The
drop of 15C is an indication that the pump cannot get enough water to
it - 11C drop is ideal.
Your radiator though is bigger and is off the scale with regard to use of
8mm pipe (see below). Basically a narrow pipe offers higher resistance
not only because it is narrow, but because the water has to travel faster
to supply the required amount to your radiator.
So while I'm coming to the conclusion that my system would be
better with a bigger pump I would bet that a 6m head pump would not
help you at all, and calculations suggest that you should use as much
15mm copper as you can.
If you do replace the pump and it solves your problem I'd love to know.
(Technical stuff: I got my data from "copper tubes in domestic heating
systems" easy to find with Google. Your radiator will require approx
.07kg of water per second from comparing it with mine. This is off the
scale for 8mm and quite high for 10mm (see table 2) - about 3m head
for 15 metres of 10mm copper - you have to then add contributions
from all other pipework and boiler in order to work out the required
pump rating).
thanks for the advice. I'll replumb it next weekend and post the outcome.
I replumbed with 15mm pipe all the way to and from the new rad. Problem solved. No need for a new pump.
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