Questions on blockage possibly made worse by power flush

Since i moved into my flat the main bedroom radiator has had trouble heating up fully (i tried bleeding, balancing, cleaning, etc). In March this year i got a plumber to do a power flush which helped the problem and it now heats up fine, though it was just in time for warmer weather so didn't use it much after that.

This winter it seems that 4 radiators aren't heating up at all, which are the 4 furthest from the boiler. I previously had similar issues that were fixed by balancing the system but that didn't help this time. So i tried taking the nearest cold radiator off to give it a hose through inside but seemed clean.

While it was off I opened one of the valves and opened the filing loop a little to make sure water was coming through, then did the same on the other valve. Both had water coming through but the water from the flow was thick with sludge whereas the return wasn't so bad. I let both run for a while until it was clearer but it still didn't get hot when i put it back on.

So I'm thinking maybe the power flush in March might have just shifted a blockage from the bedroom and it's now blocking these 4 heaters, so I've put some x400 in the system and will try to clean it out in a couple of weeks.

So my questions are

- am i right in thinking that after a power flush in March, there shouldn't be much sludge in the system after minimal use over the next 8 months?

- is it possible for a power flush to shift a blockage and make things worse? (I don't recall noticing whether these heaters worked after the flush in March)

- I've had the heating running with the x400 for over 24 hours and to try target it towards the cold heaters I've closed all others. This seems to be helping but I'm noticing that the boiler now only seems to be heating for about 10 seconds at a time so I'm not sure it's producing enough flow to get to the furthest heaters. If i open the valves on the radiators that do heat up then the boiler will run for a few minutes at a time (the thermostat is permanently on). Does anyone know why this might be happening? Does it give any clues as to what the problem is?

- the heater furthest from the boiler would previously only heat up properly if i closed most valves on the other heaters. The plumber who did the flush said this is because the pipework is all 15mm whereas it would need to be 22mm to get the required flow. Is there anything else that can be done to help this? The pipes are all in a concrete subfloor so can't be changed. Would a more powerful pump help, or maybe even an additional one?

Thanks for any help

 

Are you saying that all was well immediately after the powerflush? (just read again, and there seems to be a contradiction in your statements)

Are you saying the water is now sludged?

A PF done properly will clear sludge. If there is some sort of solid, non dissoluble, foreign body, then yes, it could be moved around.

 

The bedroom radiator was fine after the flush and still is, but I don't recall noticing whether there was a new problem with these 4 because they were ok before the flush (apart from the last one) so didn't think to check, and we didn't really use the heating much afterwards.

 

If there's still sludge in your system the powerflush wasn't done properly and you should be calling your man back to do it again. He might prove to be more difficult to persuade if you've started removing the evidence though!

 

The pump is probably still running continuously, even though the boiler is not heating. So the water is circulating.
This is happening because there isn't much flow, so the water in the boiler gets up to max temperature and the thermostat in the boiler turns it off.

 

The flow pipe from the boiler to the radiators should be hot. On a good system water temperature at the boiler should be nearly ( give or take a few degrees) or a little higher than flow into radiators

If no circulation, then either air lock or pump problems. Can be boiler too sometimes

 

Thanks, this clears up a couple of questions. The flow pipe on the boiler is red hot but today i've closed all valves apart from the furthest radiator, and the flow pipe on that is only slightly warm. So sounds like the flush didn't do its job properly and the pump is having trouble pushing the water around, so the boiler gets too hot and turns off. If there wasn't sludge i guess i should be looking at the pump for issues but i'm focusing on getting the sludge out for now

I'm a bit reluctant to get the original guy back in to have another go if he couldn't get it right the first time, plus he made a bit of a meal of it at the time (e.g left a drain valve open for a while, while running the power flush). Think I'll let the x400 work for a while then try x800 if still no improvement. Failing that I'll get someone else in.

Thanks for the help

 

I once saw a blockage in a small-bore CH pipe "fixed" i.e. dislodged by banging the pipes a lot.
If you can judge how much banging and shaking you can get away with without damaging something, this might help to get circulation going enough to help the cleaner circulate.

 

why are you dismissing the pump ???

 

I'm not, but as I understand it it's difficult to say whether there's an issue with the pump while i know there's still sludge in the system, so i'm focusing on that for now. If I were to think I've got the sludge / blockage out and it's still having trouble heating these rads (closing off all others to be sure they don't just need to be balanced), is there a way to determine whether there is an issue with the pump? Or do you just assume that's possibly the next most likely thing and replace it?

 

+1
Pumps fail... a lot!
As do mcv's. I carry 2 of each this time of year!

 

Vibrating rads (and sometimes pipework) is part of a power flush on heavily sludged systems... getting the concretions moving allows them to be broken down 'in suspension' by the chemicals.
You can do this yourself as part of a DIY, circulating or mains flush using a rubber mallet with a tea towel wrapped round it... but don't bludgeon things to death

 

I'm thinking of replacing the pump too once i've cleaned everything out, just to be sure. Not sure how old the current one is but I don't think the previous owners did much maintenance so it's probably at least 8 years old.

It's currently got a Grundfos VP5/2, does anyone know if I can just replace the head with a UPS2? Or do I need to replace it with the same model?

This is in a vaillant turbomax 824e btw

 

X400 really needs 4-5 weeks to work properly.

If you wanted a quick result you should have used X800 as that works in two hours and indeed should be removed after a maximum of 24 hours.

Tony

 

Afraid not Tony
x800 can be in the system for upto a week