Cold radiators in loft

[milleniumaire]

You could shoot the system up with mains pressure ...find a rad with a good type mt cock
connect hose with a jubilee clip and put the other end on to outside tap. close off boiler
flow and return then shoot it up with mains pressure water, start at the bottom and bleed every rad going upwards and along so the last rad is highest and furtherest away.
In case anybody wants to do this with open vented it works but be carefull not to overfill
the F & E tank. blip the pump on and off ...its a bit like heart surgery for heating systems.
then undo the lot and maybe dump all the water and do again..its not rocket science
centralheatking

It's interesting you have mentioned using mains pressure as I've read about someone doing this to remove a blockage caused by sludge.

In my attempt to remove the blockage I was going to do the following:
1. Empty some water from the CH system, enough to empty the loft radiators and loft pipe work, but ideally still keep the bedroom radiators full. This will be a guessing game!
2. Disconnect the loft radiator piping from the two 15mm pipes currently feeding the loft from the bathroom and then connect these two pipes together. At this point I have isolated the loft radiators from the rest of the system.
3. Re-pressurise the system so that it can continue to be used in the rest of the house.

I then have 2 pipes going to each radiator in the loft and I can connect, in turn, each radiator circuit to a hose pipe as you have suggested. As it is the loft, I would need a long piece of hose (just bought a 30m hose) connected to the outside tap, so I'm a little unsure what pressure I could achieve given it is going up to the 2nd floor. The other side of the circuit I would connect to a hose that terminated in the loft toilet. I can then turn on the outside tap and see if any water flows into a toilet. For the cold towel rail and cold radiator I suspect nothing will flow through. For the warm radiator I may get a trickle.

I'm not sure what the mains water pressures involved would be in doing this but suspect it will still be higher than that produced by the CH system.

If this fails I was planning to access the piping under each radiator. I haven't mentioned before, but the 15mm feed and return pipes to the loft are copper (as is the rest of the house), however, the 15mm pipes to the loft radiators are all plastic (and yes I've checked they are the correct CH pipes given this was installed 15 years ago). My understanding of plastic piping is that the joints, especially elbows, can reduce the diameter of the pipe, so I suspect if there is a blockage it is likely to be on the elbows underneath each radiator, where the plastic pipe is connected to the copper tails going to the radiator valves. Of course this is all guesswork

 

[milleniumaire]

..... I did get a company round to quote for power flushing the system as I thought this might clear the loft radiators. However, they told me it wouldn't and therefore not to waste my money, which was very honest of them!
[automerge]1571586047[/automerge]

...... Yes pipe up the loft with conventional flow and return.
centralheatking

So, the loft pipes would be run as follows?

Or, should the flow be connected to the return to ensure even when all loft radiator valves were closed, the flow would cycle back round to the boiler:

I confess, I haven't been able to find any CH diagrams that show this and maybe the "hot" water in the flow shouldn't be allowed to simply return to the boiler.

 

[centralheatking]

Yes of course set up a shoot up...in down below and find another outlet to make a curcuit
I usually put the output hose onto a hard surface ..road whatever ..so you can see what
ferric sludge comes out and when it goes clear. I have being doing this method for 20 + years
it cheap and works. basically the pump boys dont want you to know about this method
because of ££££££ it works . centralheatking

 

[centralheatking]

... I did get a company round to quote for power flushing the system as I thought this might clear the loft radiators. However, they told me it wouldn't and therefore not to waste my money, which was very honest of them!
[automerge]1571586047[/automerge]


So, the loft pipes would be run as follows?

View attachment 40985

Or, should the flow be connected to the return to ensure even when all loft radiator valves were closed, the flow would cycle back round to the boiler:

View attachment 40986

I confess, I haven't been able to find any CH diagrams that show this and maybe the "hot" water in the flow shouldn't be allowed to simply return to the boiler.

Maybe too many rads on the middle floor set up if its on 15mm flow and rtn but in principle
its all dandy ...carry on ...chking

 

[milleniumaire]

Having done some Googling, I think my second diagram, showing the flow connected to the return, is essentially a bypass at the furthest end of the CH loft piping. From what I can gather this isn't required, or particularly good practice. Also, my ecoTEC 637 system boiler has a built in bypass valve.

So, assuming I connect up the loft radiators as shown in the first diagram, if ALL the loft radiators and towel rail are closed, the flow of hot water will simply "stop" in the loft, but will continue on the first and ground floor.

 

[EvilDrPorkChop]

I'd take the rads off first, put pieces of pipe between the valves. Turn all other radiators off, make sure the water and UFH is turned off, ensure all bypass valves are closed off and run it. If the pipework gets hot then you either need to repipe in 22mm or just get a bigger pump (Grunfos do a light commerical one which is brilliant) - the latter would be your easier option.

You have to remember the pump in the boiler is only designed to give 6 meter head too so might not be big enough for your system. You will also benefit putting the pump in 100% output mode on the computer on the Vaillant boiler. The internal bypass on the Vaillant might also not be set correctly (Read the MI) however you will have to get a GSR engineer in to alter that as it requires removing the front cover of the boiler.

If it doesn't get hot at all then you've got an issue with the pipes going to the loft. If they're done in plastic they could be kinked over somewhere under a floor etc...

 

[John.g]

Also, with a cold system, the expansion vessel pressure should be > 0.8/1 bar to overcome the static head of ~ 0.7 bar due to the loft location, also making sure that the pressure is changing with hot and cold conditions in case the gauge is blocked/faulty.

 

[Stu-B]

I would try bleeding the rads at the top of the system first, air is less dense that water so all the would collect up there.