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Have a 5 yr old vokera combi boiler situated in cellar of a 3 storey house with some original 4 inch lead pipes. The pressure is always very low – about 0.5 on the dial. Get heating ok (although rads are noisy – a low hiss) and hw after about 45 secs. Should I be worried about the low pressure even though hw and heating are generally ok? Also one radiator doesn’t work. Whilst fitting a new TRV, the plumbers discovered a blockage was preventing water flow as when they took rad off and opened up valve no water came out. They suggested the system needs power flushing (at a cost of some £500!!!). Could the low boiler pressure and this blockage be related? Is there a cheaper option than power flushing? Would really appreciate any help on this. I think possibly a combi boiler is innappropriate for the size of the house!
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Posted in Discussion
you should be able to recharge the system, this is done by turning on the blue tap vavle that connects the mains water into the radiator system.
there should be a steam trap somewhere near the boiler. loooks like a y shape clean that out. you will need to shut it down till its cool .
low steam pressure would not be the problem with the radiator.Your plumber is probably right about back flushing your system.The only thing you need to know is that doing this will probably cause some water leaks in your piping. You need to be clear about who going to repair the leaks and how much.As for steam pressure have the plum er change the control that controls the steam pressure.Then set the pressure switch to manufacture specifications.
You can work backwards from the radiator they took apart. Replace piping that is plugged. Don’t know whether you have copper or galvanized but you can still replace pipe where the blockage is. Pressure on a water boiler that is low is good actually as long as the rads are working. Psi on a steam system isn’t. Make sure you continue to have ample supply of water in system. That could be problem if you don’t. You don’t need water pressure you need water volume to heat the house.
My husband says…..
If the right boiler was bought in the first place (powerful enough for the number and size of radiators), then you should be OK.
Combi boilers usually run at 1-1.5 bar.
0.5 bar Is low.
Not sure what you mean ‘always low’.Are you saying it is 0.5 all the time or are you saying you re-pressurise the system to 1-1.5 bar and it drops.
If the former, then you can repressurise the system.
There should be a pipe with a tap linking the cold water feed pipe with one of the heating pipes. Open the valve slowly. The pressure should start to rise. When it reaches 1.5 bar, turn it off. Don’t over-pressurise or you could bust a radiator.
If the latter, you have a leak in the system somewhere that is allowing the pressure to drop. Find it, fix it!!
I cleaned out my system by draining the system down and refilling with clean water and added a flushing agent (available from DIY stores). I then ran the system at maximum for a week (not good in warm weather!!!). I then drained the system down again, refilled with clean water and ran the system again on maximum for a couple of hours. I repeated the process a couple of times until the water coming out was clear. I then refilled the system again this time adding an inhibitor fluid (again available from DIY stores).
The problem with the radiator could be a sticking thermostatic valve. I had one and cleared it by taking off the adjustment barrel (you may need an instruction leaflet or try the manufacturers web site for instructions as to how to do this), pushing the brass pin coming out of the end fitting attached to the radiator in and out a couple of times with the end of the screwdriver then reassembling the valve. The radiator should then begin to get hot.
If that does not work, try opening and closing the lockshield valve (the one at the the other end of the radiator) a couple of times (you never know it may be locked closed).
Hope the above helps