To power flush or not to power flush?

Soldato
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23 Nov 2019
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One for the plumbers:

We've got a radiator (upstairs bathroom) that keeps oscillating between working normally and barely getting warm - for several days at a time. Rad is brand new, valves are new and confirmed working. Plumber thinks there may be some kind of blockage in a pipe that is building up, releasing, build up again etc. He's not sure where though. The old rad worked fine for most of its life then started doing the same after the valves were changed to thermostatic ones hence we got the rad changed. We've also had the valves swapped again just to make sure it's not those either.

I'm not sure what our options are and what the best course of action is.

Should we just get the system power flushed, and is that the right thing to do? Am I right in understanding it's just shoving water through at high pressure? Any risks to that eg bursting joints, resulting leaks etc? Are there any alternate steps we could/should take?
 
Soldato
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Power flushing is a good way to clean your system out. But yes it can show any weak points in your system, particularly if it's old.

I would leave a system cleaning solution in the system for at least a week before power flushing. If you want to do the job right, take each radiator off the wall and clean it outside with a hosepipe. Then do the power flush to clean the rest of the pipes out.

Once the power flush is complete, install a filter in your system if one isn't already installed. While topping up your system, put some inhibitor in your system to help prolong it.

I'm not a plumber, but I speak from experience. Taking radiators off the walls isn't as scary as it sounds. Just beware that the large radiators can be quite heavy and might even need two people to lift and manoeuvre.
 
Soldato
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There's a voice that keeps on calling me.
I had a really bad blockage years ago, a portion of the house would never get warm. Turned out to be a T under a floorboard was letting a pin hole worth of water through. Finding it was a case of following the pipes and using a magnet to find the blockage. A powerflush would have struggled to move that tbh. I'd remove the worst rads and hose flush them, you could also close of the boiler and put a hose on any drain of points and try and get things moving with water pressure. Also if you have a rubber mallet try tapping the rads to get the old sludge moving.
 
Soldato
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Thanks everyone, really useful. System has inhibitor in it already. All the upstairs rads (bar one) are new, it's just downstairs still to be changed. The one we kept is working fine so we probably won't move it as we've just finished decorating that room and the new carpets fitted in there. With all the furniture back in we can't really get good access to it, not enough to remove it and get it outside easily anyway.

The blockage doesn't seem to be in the rad itself. So far as the plumber could tell it was under the floor, possibly under the bath itself. There's a donkey show of missing floorboards and pipe spaghetti under there to make you weep. I'll see if plumber can recommend a cleaning solution to throw in it for the weekend and christmas period as I doubt he'll have availability this side of the holidays given timing and the ever increasing restrictions etc.
 
Soldato
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I've used Fernox f3 in the past. If you have a filter in the system then it's easiest to pour in there.
If that doesn't shift it then I've cleaned out a full system in the past by closing off the valves to each radiator, removing each one and flushing them out in the garden until the water runs clear then attached the hose to the system on one of the radiator inlets with another hose for a drain on the outlet and then opening both valves so it flushes the main run and the two pipes to the radiator, do this for each radiator location and you clear out the main pipes and each radiator location one at a time, takes a while but was well worth it.
 
Soldato
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dumb question but how do I tell if I have a filter already? What should I be looking for, and where in the house would it be? By the boiler or in the loft etc? We're on a gravity system with tanks in the loft. Boiler in GF kitchen.
 
Soldato
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It should be fitted right next to the boiler (on the return pipework I think) mines a magnaclean. It'll have a shut off valve either side of it so you can isolate it and unscrew the top cap without flooding your house :D

Just checked and yes it should be fitted as close to your boiler as possible on the return line, it can be fitted elsewhere if it would make it inaccessible though.
 
Associate
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Check that your heating system doesn't have any plastic push fittings as too high a pressure flush can blow weak or poorly made joints.

If you can get hold of a thermal camera these are brilliant for finding poor flow and low performing radiators.
 
Associate
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If it only happened after getting thermostatic valves fitted then it could be that that radiator has been plumbed in in series so it's only getting heat when the thermostatic valve on the radiator that's feeding it is open.

What happens if you fully open all/remove the heads on all of the thermostatic valves?
 
Soldato
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Check that your heating system doesn't have any plastic push fittings as too high a pressure flush can blow weak or poorly made joints.

If you can get hold of a thermal camera these are brilliant for finding poor flow and low performing radiators.

a power flush is under no more pressure than a normal sealed system
 
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