DIY Doctor UK DIY Forums

I have an older property with a 22mm single pipe central heating system.

All radiators seem to work reasonably, but on taking up the floor near one I found the 22mm pipe had been 'pinched' (presumably with a pair of grips) between the points where the feed and returns (15mm) to the radiator T off from the 22mm pipe.

I think I can understand the physics - the water finds it easier to go straight through the 22mm pipe without 'bothering' to go up through the radiator and back down again, so the 'pinch' acts like a crude reducing valve to force more water up through the radiator.

I'm certain the floor has never been up since the system was installed in 1968, so I'm assuming the installers must have done this, and that the valves on the radiator were new at the time.

'Pinching' the pipe like this must weaken it somewhat, and I'm worried a leak might develop, and be hidden for ages until it does real damage.

I'm guessing a better way is to run 15mm pipe, instead of 22mm, between the two Ts, but is that acceptable, and might it put unnecessary strain on the pump if the radiator is turned off?

I know single pipe systems are pretty obsolete now, but has anyone installed one, and how did you get around the problem I have described in a more professional way?

Thanks for any help.

jackthebuilder,
Replace the pinched section of pipe with a ballofix valve which you will then be able to adjust for the flow which suits your needs best.
end

Thanks Stoneyboy, but when the floorboards and carpets are back down I can't get to it to make any adjustments - yes, I know it's probably the same as I have at the moment, but I just get twitchy about putting in valves that I cannot access.

So let me get this right, your worried that a plumbing system that has worked fine for 40 years without leaking is suddenly going to fail?

Well, you have a point about the damage crimping the pipe has done, but as it has lasted so long, I would say it is no more likely to fail as any other part of the pipe work. Remember, copper pipe was much thicker in those days so damage is possibly minimal. Consider as well, if you fiddle around and replace bits there will very probably be a greater risk of the new joints leaking than there is of the old stuff letting you down. Oh, and it's probably 3/4" not 22mm too!

I would suggest, replace the whole lot for a proper efficient two pipe system or leave well alone. I can't see any reason to tamper with it.

Thanks plumbbob - on looking at it that way, I feel a bit of a wally!

I actually have 2 properties, both single pipe, and it's only because I have just found similar problems in the second property that inspired me to seek advice!

I seem to recall that there was a copper shortage back in the late 60s, and remember the installers at the time saying they had to use some form of 'copper substitute' for some of the installation. I see some references to that shortage on the web, but no detail about the composition of any such 'substitute'.

Both properties have more than 14 radiators - I've seen comments that 2-pipe systems are not as efficient for larger installations - any comment?

Thanks again.

Oh, you will recognise the "substitute" pipe as soon as you see it. It was steel so all the pipes are silver. As you can't solder steel, the joints are all compression which is actually it's weakest point.

It is standard 15 & 22mm in size, but has to be cut with a hacksaw as it will instantly ruin a traditional pipe cutter.

"I've seen comments that 2-pipe systems are not as efficient for larger installations"

Really? I believe the opposite is true. The more rads there are on a system, the greater the temperature fall between the first and last on the line.