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!
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
You need to repressurise the boiler asap. 0.5 is far too low and the boiler will cease to fire if it drops even slightly lower. You need to aim at 1.0 to 1.5 bar in the cold state. Read your manual on how to do it or go online for the instructions. It only invokes opening a valve or a pair of valves under the boiler. Nothing difficult. With regard to the blockage. You don't need to power flush. Wait until the summer and disconnect the TRV from the radiator. Turn up the system pressure to max which is probably about 2.5 bar. You can't do any harm as the safety vale will vent to outside the building at about this figure or just above. Holding a bowl in position open the TRV slowly and hopefully a slug of sludge will emerge. If it doesn't you need to release the pressure via a bleed valve, remove the TRV and get someone to turn up the pressure again whilst you poke a bit of wire along the pipe. Be prepared for a sudden deluge and catch it in a bucket. It will only pour out for a very short time as the pressure will drop quickly. Then add chemical cleanser to the system, flush and refill with inhibitor. I know it is a fuss but it beats paying them ?500 and you will have done a better job anyway. See the link for procedure. There is also a pic of a filling loop which your boiler may have.
Bleeding the radiators may help, but consider an annual; service of the boiler, which will reveal the problem. Flushing at ?500 seems rather expensive. Combi boilers are pretty reliable, but worth checking with an engineer as to whether the boiler is adequate for the number of radiators in the property. You may get this info from the manufacturers website.
