Strange problem - 2 cooler radiators

marksi · 26 Jan 2006

House is 10 years old, plastic microbore pipes, oil fired boiler. System is pressurised at 1.5 bar. Pump is turned up full (3). There are four radiators downstairs and 4 upstairs. A main feed comes from the boiler in a large pipe which splits into two... there is then a 4-way manifold on each pipe, one feeding upstairs and one feeding downstairs. Each radiator (except one) has a TRV on it and they were fitted when I moved in last year.

I have one radiator on each floor which is cold (or rather, not nearly as hot as the others). They have been cleaned out and it's been confirmed that the pipes are not blocked. There appears to be no flow across them - the valves and a little area at the bottom of the radiators are hot, but the rest of the rad is only tepid. All other radiators are very hot. System is balanced, and turning off other radiators doesn't appear to make any difference to the flow across the two which don't work.

Now completely stuck for ideas on what to do next, plumber has suggested replacing all the pipework which I don't want to do as it'll cause every room to be upset (not to mention the cost, which I can't afford). Help!

Bahco · 26 Jan 2006

If no blockage, the problem must be a circulatory one. Is the pump working correctly?

You could try changing the microbore, feeding the problem rads to 15 mm, branching off the 22 mm F & R.

marksi · 26 Jan 2006

Pump appears to be fine - if it wasn't working surely there would be a problem with tha rads in other areas... the two that don't work have shorter runs than some others which are perfectly ok.

Bahco · 26 Jan 2006

You have bled them, yes?
Valves are fully open?
How do you know system is balanced?

Have a look in the reference section above and see if you have missed anything.

marksi · 26 Jan 2006

Bahco said:
You have bled them, yes?
Valves are fully open?
How do you know system is balanced?

Have a look in the reference section above and see if you have missed anything.

They have been bled, yes. The valves are fully open on the two radiators concerned. Even when all other radiators are off, the two radiators in question do not get as hot as the other radiators in the system.

dal5band · 26 Jan 2006

Someone had a cold rad in the basement problem and I think Fitz1 suggested :

"turn all other rads off.possibly air in return,should push it through"

Try this with one of the problem rads. With all the flushing and cleaning you've had there is probably some air trapped somewhere. Full force of the pump should clear it.

marksi · 27 Jan 2006

dal5band said:
Someone had a cold rad in the basement problem and I think Fitz1 suggested :

"turn all other rads off.possibly air in return,should push it through"

Try this with one of the problem rads. With all the flushing and cleaning you've had there is probably some air trapped somewhere. Full force of the pump should clear it.

Have tried that. Didn't work.

I should say that the one with the problem downstairs (kitchen) only gets luke warm, the problem one upstairs gets hot, but not as hot as the others and takes quite a while to get that hot.

I did try Fernox Restorer in the system and ran it for a week before flushing. Should I have left it longer? Would it have done any damage to leave it in permanently (in place of the normal Fernox)?

The plumber I had round says the only solution he now has is to replace all the microbore with 15mm. Is he likely to be correct, given that the house is only 10 years old?

Given that the rest of the system seems ok, would you recommend replacing ALL the microbore or just to the problem rads? If I only change the pipes to the problem rads will I just end up with the same problems in other ones?

marksi · 28 Jan 2006

Oh, and while the kitchen radiator has never worked properly, the upstairs one goes through periods of working correctly and not, should that provide a clue...

All help very much appreciated.

dal5band · 28 Jan 2006

I just realised you have TRVs - there was someone saying that a TRV can get stuck with age & gunge. If you carefully remove the head of the TRV, (Usually a metal collar near the bottom) there is a spring loaded pin sticking up. The spring is supposed to push the pin out (up) to fully open the valve. Press the pin down with the flat of a screwdriver and make sure it springs out fully when released. Put a drop of oil and work the pin in/out a few times to get it fully open. If when you first see it it's a bit sticky and slow to come up - this could explain the erratic behaviour.
Ensure you put the head back on with the valve in fully open position.

marksi · 28 Jan 2006

TRVs are all brand new, and I've checked them... they don't appear to be stuck. The pin is moving up and down as it should.

bab · 28 Jan 2006

U say if u turn all other rads off they still dont get hot,When they took off the rads to flush them out did they open the valves ito a bucket & draw lots ot water through to prove the pipe supply did they flush out the rads outside with a hose pipe to ensure clear tails & water ways. If so theres sumut strange goin on. u shouldnt need new pipes If it worked once it should work again.

marksi · 28 Jan 2006

bab said:
U say if u turn all other rads off they still dont get hot,When they took off the rads to flush them out did they open the valves ito a bucket & draw lots ot water through to prove the pipe supply did they flush out the rads outside with a hose pipe to ensure clear tails & water ways. If so theres sumut strange goin on. u shouldnt need new pipes If it worked once it should work again.

With the one in the kitchen, it was taken off and flushed out with a hose. The filling loop was turned on with a hose attached to the return pipe in the kitchen and there did appear to be plenty of water coming out of it. I don't remember him then checking the flow pipe (though there is about an inch of the rad at the flow end which is hot). Could there be crap in the manifold just blocking one of the pipes? Do I need it powerflushed, and if so, does anyone know of a company in the Belfast area which does it?

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Strange problem - 2 cooler radiators

marksi

Bahco

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Bahco

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dal5band

marksi

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dal5band

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bab

marksi

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