Flushing pipes and radiator?

Problem
A radiator attached to a pressurized, combi-fed, central heating system doesn't get hot (it gets just slightly warm).
- I've bled it but this makes no difference.
- The radiator is fed from what is essentially a spur off the same pipes as a second radiator, which does get very hot. Turning this "hot rad" off, in the hope that all the water will go to the cold radiator, doesn't achieve the desired result.
- I've checked and now both the radiator tap, and the valve at the other end, are full open (assuming they're working - perhaps they're not?).
- Finally, this radiator is on the ground floor, but fed from the first floor so crap could easily be coming down the pipes, blocking them and never getting away again.
So, what next? "Reinstall the entire pipework" is not an option so I intend to "flush" the pipework. Before I start, any tips? I'm planning to (after turning off the heating)...
1. Close of the pipes to the radiator (there are values which allow this - no idea why they were originally installed!)
2. Close off the radiator taps
3. Remove the radiator
4. Flush the radiator with a hose
5. Connect a hose to the radiator taps
6. Get the wife to open the radiator taps whilst I maintain pressure using the "fill" loop from the boiler. I'm hoping this will provide enough pressure to flush crap out along the hose and clear the taps.
7. Replace the radiator.
Clearly I'm no heating expert, but any suggestions for making this as painless an exercise as possible would be appreciated.
Thanks, Paul DS
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Sounds fine but why not try it with the radiator still in place to start with?
Points to note:
1. You'll need to find (or fit) a drain point to get rid of the flushing water.
2. You'll need to isolate the boiler in order to stop the flow going through it instead of flushing the rad and to stop it filling up with crap. Some boilers have isolation valves but I just fitted a 22mm full bore ball valve in the return of mine to do this.
3. Close off the rad valves to all the rads you don't want to flush then open up the filling loop to flush through the rad in question, being careful to watch the pressure and ease off before the system pressure relief valve pops off at 3 bar (avoid this as any crud in the system may affect the sealing of this later).
4. Repeat for each rad in turn if you want.
5. You may wish to run the system with some flushing fluid in it for a day or so before you do this as it will loosen up any crud. Alternatively, try this first to get some flow going, then use the flushing chemical as the chemical wont reach the blocked area until you get some flow going.
6. If this fails then take off the rad but protect the room like a scene from Dexter, plastic ever and old blankets to mop any spills (they will inevitably be black (iron oxide) and will stain anything they touch). Invert the rad before moving (open ports to the top to avoid the risk of spills).
--
fred
it's a ba-na-na . . . .
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On Wednesday, 12 December 2012 12:37:07 UTC, fred wrote:

An Aqua Vac or similar is very handy for capturing the water to be drained from a radiator. Close the inlet/outlet valves and, with vac running and held near the TRV, gradually undo the TRV-to-rad coupling. The water will start to trickle out and most will be caught by the vac. If you are feeling brave you can increase the flow by opening the bleed valve.
Richard
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On 12/12/2012 11:38, Paul D Smith wrote:

If they are conventional taps then its rare for them to fail stuck - especially if they feel like they are working and wind from closed to open with a definite stop at each end. (if the handle twiddles endlessly then that is a different matter).
With thermostatic valves however, its not uncommon for the pin to get stuck down in the closed position. Taking the head off the valve to check will usually tell you. Sometimes the pin is of a design you can grab with pliers and work free. With some a sharp tap from a small hammer will do it.

Valves perhaps? What sort of valves? and are you sure those are working?

Yup if you make up an adaptor to connect the hose to a valve, then you can flush from the filling loop and out the hose. To concentrate efforts on just that rad you will need to close the valves to all the other rads - then you can have full mains flow through that pipe. Do the same for the other rad tail.

It sounds like you are on the right track.
An alternative slightly less complicated method to try first might be to connect a hose to the normal drain point, open it and then turn on the filling loop. If you have shut off all the rads except the one in question, you should force through any blockages and give it a fairly decent flush into the process. (wait until the water runs clear - which may take several minutes)
--
Cheers,

John.

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I've had a couple of cases of gate valves which could be screwed closed, but not opened anymore as the gate was no longer attached to the shaft. You can't directly tell this without removing them for a post mortem, although you might infer it from other indications of a lack of flow.
Now all replaced with full bore ball valves (although you have to remember to operate these periodically, or they seize up).
--
Andrew Gabriel
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On 13/12/2012 10:41, Andrew Gabriel wrote:

Yup, been caught by that a few times!

I think on this last fiddle I managed to eliminate most of the gate valves... IIRC there is only one left now, and only after I had the system all up and running did it dawn on me that its actually pointless anyway as its after the zone valve on the cylinder heating loop - presumable installed in the original system to allow the cylinder circuit to be balanced with the rads. Since the new system never runs the rads and cylinder at the same time, its more decorative than anything else!
--
Cheers,

John.

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...snip...
OK, this might help someone! Tried to sort this out and discovered...
1. Neither gate valve seals, so they're a complete waste of time.
2. I cannot get the water out of the pipework without totally draining the heating (see #1)
3. I did managed to get a drain cock which fits into the radiator where a bleed valve would sit. I managed to fit this buy turning off both radiator valves, checking the bleed valve to confirm the radiator valves had sealed, and then fitting the drain cock (needing some of that sealing goo around the threads).
That was the good news - the bad news was that on turning on the radiator valves (independently) with the drain cock open and my wife working the filling loop to maintain pressure, one site of pipes flushed nicely (black crud all round) but the other flowed slowly for a while and then blocked completely.
So, off to get the nice plumber out. Emptying and sorting this is within my skill range, but a professional will do it quicker, better and will know how to sort nay more gotchas (I hope!).
Paul DS.
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