Cold downstairs radiators mystery??

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29 Jan 2006
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Location
Manchester
Country
United Kingdom
Boiler: Baxi WM 51/3RS
Prog: Potterton EP3001
Pump: Grundfos ups 16-60
M-Valve: Sunvic SD 2701
7 Rads all with TRV
3 bed semi with Hot Water Tank.
=================

Last week the downstairs radiators stopped working all of a sudden.
I did the normal easy thing and bleed all radiators but to no avail.
I checked the pump (opened the screw, popped a screwdriver in it and it is running)
Turned the the pump from 2 to 3. Speed increased but still no heating downstairs.
Next I turned the upstairs rads off and the downstairs rads came on!
I rang a heating engineer up and he said if the pump is running it is probably sludge build up. (i have however flushed out every rad in the last 4 years when decorating)
He recommended SM4 Sludge Remover. So I drained the system, added the SM4 to the header tank, ran the CH for a week then drained the CH until the water ran clear (took about an hour). Filled the system back up with water and inhibitor (SM1) and bleed all the radiators.

However, as you have probably guessed it has made no difference. The rads are still cold downstairs if the upstairs are on. Even the pipes feeding the TRV's downstairs don't get hot until the upstairs rads are turned off.
Also, the larger rads downstairs don't get exactly red hot and they are colder at the bottom.

Can the pump be failing to 'pump enough' even if it is running?
Any ideas?
 
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have to tried balancing the system

IE turning the lockshield rad valves on the upstairs circuit down a tad and see if you cab force the downstairs to heat up?
 
corgiman said:
have to tried balancing the system

IE turning the lockshield rad valves on the upstairs circuit down a tad and see if you cab force the downstairs to heat up?

Thanks I'll give it a go.
But why would the system fall out of balance literally overnight?
 
because black magnetite is building in the system and creating a greater resistance to the downstairs circuit
 
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corgiman said:
because black magnetite is building in the system and creating a greater resistance to the downstairs circuit

Ok. Thanks.
I have just set all the upstairs lock sheild valves to half turn open. They were all open one full turn.
All downstairs rads are open one full turn.

I'll see what happens.
 
I'm really scratching my head now.

I tried turning each upstairs locksheild valve down to 1/4th or 1/8th turn and a little bit of hot water got to the rads downstairs but nothing major.

I the process off playing with the system, I realised that the motorised valve was knackered as the water temp was getting up to 80+ degrees and ignoring the hotwater cylinder thermostat.
I have now replaced the 3 way Motorised Valve and for good measure i changed the pump as well (DAB type) as they are next to one another. But guess what, the problem remains.

The only way to get any hot water into the downstairs rads is to turn off the upstairs rads. I have also noticed that if i have a bath, the downstairs rads turn off as I guess the Motorised valve moves to the mid position thus only 50% of the water pressure is directed to the CH system and is not sufficient to get downstairs.

This leads me to believe that it MUST be a circulation problem or partial blockage with the downstairs circuit that is restricting flow.

I have tried SM4 in the system for a week I now I have 'Fernox Central Heating Restorer' in. I am running the system with the upstairs rads off permanently hoping the circulation problem on the downstairs circuit will be flushed out with the fernox.

Sorry for the long post but if anybody can advise on the next cause of action it would be much appreciated.
 
Went to one today with the same problem. I asked if the problem had just suddenly happened or had come on gradually. I was told it had just happened. I went to the pump took the cover screw off stuck a small screwdriver in and freed the impeller. After turning the pump speed up a notch hopefully that will keep them going till I get round to fit a new pump.

If it had come on gradually I would probably be looking at a sludged up system
 
Thanks for the reply.

However, i'm doubtful that it is sludge because I have taken every radiators off in th elast 4 years and flushed them out.

I even drained the CH system a couple of weeks ago and left the water running through it until it came out clear.

Could it be an airlock or some other strange phenomena?
 
Thanks but I changed the pump last weekend but the problem persists.

I have read through all the forum posts with similar probs and people seems to suggest the following:

1. Turn down the Locksheild valves upstairs. - (I've done it)
2. Drain the CH system, run the water through until clear then refill. - (I've Done That)
3. Change the pump. - (I've done that)
4. Run with SM4 sludge remover for a week and drain. (I've done that)
5. Run with Fernox Central Heating Restorer for a week and drain. (I've Ran it for a week and I plan to drain it this weekend)
5. Get a powerflush. (I only want to go down this route if it solves the problem as it is very expensive)


At the moment i can get away with running 1 rad upstairs and the downstairs remain on. But if i turn a second rad on upstairs, non of the downstairs come on. This can only lead me to thhink that the flow to the downstairs circuit is restricted thus the water is taking the easiest route. (i.e to the upstairs circuit)

Any additoonal help would be great.

PS Has anybody had experience where powerflushes resolve this type of problem?
 
just to check, when you replaced the motorised valve, it was the valve part you changed, not just the motorised head?

Your bathroom radiator, is it plumbed so that it comes on when you are heating hot water, or only when the CH is on? If the former, try actually turning it off. If that helps, ease it back just a fraction with the lockshield very near shut. Sometimes bathroom rads can take a lot of flow, especially if their TRV is set high.

Are you still finding the hot cylinder gets very hot?
 
Thanks for the reply.

Yes, when I replaced the 3-Way Motorised Valve i changed the complete unit (valve and head). It was a sunvic 2701 and is now a Honeywell model.

As far as i know, the bathroom rad is plumbed in like the rest off the rads. i have never noticed it come on just when the water is on. It is the closest to the pump and does get hot quicker then the rest but i have the locksheild valve at 1/4-1/2 turn and the TRV set to 2.

Yes. Even though i have changed the MV and the cylinder stat, the hot water gets hoter than it should but only when the i have a couple of upstairs rads on and the downstairs aren't on/not working. It's like the water has nowhere to go in the CH system (due to a restriction) and seems past the MV to the hot water cylinder.
 

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