DIY Doctor

Oh Why on Earth ???/

Postby bmwnunkie » Sun Nov 18, 2007 12:20 pm

Long story... but.. in essence builder chappies have taken off ALL the downstairs radiators ( we have been flooded and the downstairs ruined ). However, we thought it prudent to put the rads back on in order to keep the ground floor warm during cold snaps etc. I have done this and bled them ( they are full of water ). The problem is that they will not run hot/warm when then upstairs rads are fine. Upstairs is 15mm piping and downstairs is 10mm microbore. If I open a drain tap attached to one of the downstairs rads... it will pour out hot water after a second or two. Once I close this off the rad, in question, will be warm/hot for 10 minutes then go cold again. WHAT IS GOING ON? WHAT AM I MISSING ?

Sitting in a caravan... in the rain... cold,fed up, wet with house like a bomb site!!
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Simply Build It

Postby Nimrod » Sun Nov 18, 2007 5:15 pm


Sorry to hear that you are suffering so much grief. I know from experience how cold caravans can be.

At least two possibilities suggest themselves and I apologise if you have already considered these.

1. Could there be a valve(s) that isolate the upstairs 15mm circuit from the downstairs 10mm circuit that just needs to be located and opened? Are all the valves open on the 10mm circuit.

2. The water flow needs to be balanced between the two circuits. The 10mm will have a higher resistance than the 15mm one.

I suggest you first turn-off all the radiators on the 15mm circuit.

Open fully all valves on the 10mm circuit. If the downstairs rads get hot you know your problem is due to imbalance.

Return upstairs and open slightly the valves on this circuit. Shuttle between the two until you get the system stable.

Good luck

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Postby Perry525 » Sun Nov 18, 2007 8:53 pm

Close valves on all but one rad upstairs.
Open valves both ends of each rad downstairs.
Turn on heating.
If the downstairs rads don't run hot.
Check pump.
Check 22mm pipes out and back to boiler.
Is hot water getting round system?
Have you rebalanced system diverting all hot water upstairs while downstairs was unused?
Is hot water merely taking the easy route through the 15mm pipes?
Is the system zoned?
Has a motorized valve stuck/died?
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Postby marrtin » Sun Nov 18, 2007 9:36 pm

It could be an airlock blocking the flow of water, switch off all the hat rads to see if this will push the air through.

More likely, especially as you mention that the downstairs are fed by microbore pipes is the heating system needs balancing.

See Central Heating - balancing in the DIY projects section of this webisite.
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Postby DONFRAMAC » Mon Nov 19, 2007 12:32 am

Shut off all the upstairs rads., both valves, then do the same downstairs, except for one. Open its valves fully and bleed it. It should give flow and heat,top and bottom. Open another downstairs one, and almost ctose the simple isolator valve on your first success, retaining some flow. Establish flow one by one downstairs, throttling-down flow as you go. this is known as balancing rads.
When you return upstairs, the 15 mm bore will require less opening turns of the isolator valves, and of course the thermostatic rad. valves will only need settings of 4 or thereabouts.
Rads. that stay cool along the bottom, indicate sludge, which could well be a problem enhanced by microbore, but can be flushed, or powerflushed (costs £600).
Air-locking could still exist despite the above work, and could be shifted by a plumber.
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