Cold Radiator - thwarted

[D_Hailsham]

The boiler is a Potterton Suprima 80L - the pump is grundfos p/n 59506151

The flow rate at max output is 0.51 litres/sec and the available head from the pump is 3.5m (see chart below). The pressure drop in the boiler is about 1.1m, so there is only 2.4m available for the index circuit. Your system could well exceed this, given the number of rads and the convoluted pipe runs.

(click to enlarge)

Untitled

• D_Hailsham
• 28 Oct 2013
• 1

The solution is probably a larger pump , but you should try balancing the system first.

Remove any TRV heads first and set all wheel valves to max.

A reasonable balance can be obtained by setting all lockshield valves to about ⅓ turn open from closed. Open, slightly, the LS valve on any rad which appear to be too cold; and close, slightly, those which are too hot. All rads should feel about the same temperature.

The fact that the rads have a slightly greater output than the boiler should only have an impact if you are heating the HW cylinder when the heating is on.

edited by D_Hailsham: 'cold' changed to 'closed'

 

[BobbyOllox]

thank you for the advice. I may just have to upgrade boiler and pump to cope with the system

In the meantime, I flushed out the flow pipe, and refilled the system ( didnt appear to be any significant discharge). Three radiators refused to get warm including the rad in question.

Emptied and refilled again - better but not as good, and the rad in question is back to being tepid warm.

Wondering whether this whole issue is made worse by some obscure airlock. Sorry for jumping around, but it is so confusing.

Thanks for all your help everyone - going to sleep on it - maybe the plumbing faeries will fix it overnight.

 

[xr4x4]

Have you turned off every single radiator except the bad one?

And the made sure the hot water is off?

If its a vented system, have you tried pumping cold mains in the top of the rad via a hose pipe? May dislodge a stubborn air lock.

Any other bleed valves on the pipework?

 

[BobbyOllox]

OK - I was tired - false alarm - I had left the boiler on minimum.

So today a new day - all radiators hot except for the rad in question still. When I turn off all other rads, ( except 1 which the TRV doesnt close), the rad gets hotter than it has ever been, but not as hot as other rads - still the return pipe immediately out of the rad is tepid.

To summarise
changed rad - brand new
changed valves at both ends - brand new
proven good flow along flow pipe - removed rad and ran mains water through flow supply and out.
proven good flow along return pipe - ditto as flow pipe, and system drains out of valve on return pipe
rad will drain out through valve so no blockage in new valve at return end.
DH - calculates need a bigger pump and recommends balance system. ( I accept that - but even with majority of rads off, boiler on max heat, the return is never more than tepid, the flow can be too hot to hold. )

Boiler is in loft space, bad rad is on ground floor ( but so are many good rads) - pump is next to boiler, on the flow side.

22mm pipes from boiler to 1st floor, and around 1st floor - 15 mm to ground floor rads.

 

[D_Hailsham]

When I turn off all other rads, ( except 1 which the TRV doesnt close), the rad gets hotter than it has ever been, but not as hot as other rads - still the return pipe immediately out of the rad is tepid.

Turn of the LS valve on the one with a faulty TRV. It might even help if you turned off all LS valves - except the one you are testing, which should be full open.

If you still get no result, but the flow is hot and the return tepid, the only thing it can be is a blockage. But this would cause the boiler temperature to rise rapidly and the boiler shut off by the boiler stat.

 

[BobbyOllox]

thanks again DH

no sign of lockouts at the boiler, but I have to agree that a constricted flow somewhere is the logical assumption - but b**gered if I can figure out where

This is a schematic of the rad layout

View media item 68423
this is a ( poor ) diagram of the layout of the pipework to the rad.

View media item 68424
I have disconnected rad and the pipes at a and b and done bidirectional hosepipe tests on each . . So if it is constricted it is upstream of that. I may just have to live with it, as I really dont want to start lifting carpets and floor boards.

 

[D_Hailsham]

View media item 68423

I have disconnected rad and the pipes at a and b and done bidirectional hosepipe tests on each . . So if it is constricted it is upstream of that. I may just have to live with it, as I really dont want to start lifting carpets and floor boards.

I assume you mean that you have tested the pipes which go round the floor from a and b to the rads.

As the two ground floor rads and one first floor rad to the right of the cool rad are heating up OK, the only place where there could be a blockage are the two pipes dropping from first to ground.

You could test them by disconnecting at the rads, instead of a and b, and timing how long it takes to fill a bucket.

 

[BobbyOllox]

Can you give some details on how that works. What am I looking for ?

thanks

 

[xr4x4]

Try this, or some of his other videos on cold rads.

http://www.youtube.com/watch?v=bAeRurEExBs&feature=youtube_gdata_player

 

[D_Hailsham]

Can you give some details on how that works. What am I looking for ?

I'm suggesting you do the Bucket Test; Andy (Herts Drainage) suggested this on Thursday.

So far all you have tested is the flow from a to b through the rads, which has been shown to be OK. The bucket test will test the flow, in each pipe, from the first floor Tee junction to the rad valve.

You need the flow to be approximately equal. If one is much slower than the other, you have a blockage in the vertical riser from a or b to the first floor, or in the Tee connection.

 

[BobbyOllox]

thank you I had missed that reference - thanks to you both for the suggestion. Seems obvious really in retrospect.

I will try it - unfortunately I will be away for a few days, but will try on my return.

Thank you also Paul - I found those series of videos excellent - I closed the rad valves, and ran water out of the retutn pipe drain, until hot water from the the system flowed out - no sign of airlock there. I have assumed no airlock on the flow side since hot water reaches but for completeness I should try do similar on the flow side. thanks

( by the way DH - I had removed the rad and made 4 tests - rad to a, a to rad, rad to b, b to rad - never tried a single test of a to b - again for completeness I should do that also )

 

[BobbyOllox]

Completed the bucket test ( rad off, run water out through valves from flow and return) - the return had noticeably more force - it filled the receptacle that I was using ( about 2.5 litres) in 20 - 25 secs, whereas the flow pipe took about 50 secs.

( btw - I did the flow first, then the return, then repeated a couple of times until the pressure dwindled as the system emptied - so it does seem that flow flows slower than the return )


So I guess there is some issue in the flow pipe after all ( or maybe both ? ) Would that be right ?

My mains pressure is not strong and the gravity flow does not seem to have dislodged whatever is slowing the flow. What are my options ? Is it time for a power flush, or are there other tricks I could try.

Really appreciate all the help you have given me so far.

 

[HERTS P&D]

Do a mains flush.

Block the vent and feed on the loft.
Fix a hose pipe to one rad valve and lead in to the garden then fit your hose pipe to the other rad valve and turn on the hose.

Then swap around and flush the other way round.

Andy

 

[BobbyOllox]

OK I will give it a go - assume makes no difference that it is a non-vented system.

plan to turn of all rads first, so is just pipework that will get flushed - correct ?

Mans pressure here is not very exciting - dont know if it will be strong enough to push anything.out.

thanks

 

[BobbyOllox]

Mains flush completed - 15 minutes each way. No spectacular purge of sludge, but end result is that the radiator is hotter than I have ever been able to get it.

After the flush, it took ages t get warm, and in the end I switched off all other rads - then it got hot - I opened other rads, and it stayed hot.

Here's the thing - during the flush, I closed all the rads, but then I realised that another radiator on the same circuit was still open ( knackered TRV ), so I closed it at the LS. I am fairly sure that when I closed it that the flow out of the feed pipe at the bad rad stopped to an absolute trickle , I tried opening and closing the LS at the knackered TRV rad a few times, and I am fairly sure this would repeatedly stop and start the flow at the feed. In the end I think the LS stopped closing properly ( its old) so I couldnt replicate any longer - but I dont think I was imagining this.

Ive tried to figure out what that would mean - I think it means there is a block somewhere on that circuit . ( and also I got my diagram wrong)

Anyhow, will monitor it over next couple of days - its not perfect, but if it stays like this I can live with it. If not, I will have to get a pro in to powerflush the pipes. and of course I now need to put new valves on this other rad which I cant turn off now.

Thanks all for all your advice - if any of this update makes you go ah-ha , then pls advise, otherwise I think my missus has run out of patience now, and its time for a pro.