Central heating on blink for a year: help pls

[indiegrrl]

Moved into our house yr ago. Ageing Vaillant boiler, constant v low pressure on boiler, low heat in radiators and no heat in a couple (one upstairs, one down). Needed replacing anyhow, got it replaced w Worcester Bosch by a specialist, but pressure remained low. Worcester have checked boiler, plumber has checked boiler outlets, all fine apparently. Plumbers have drained system, cleaned out system, replaced 2 radiators, bled all radiators, finally isolated central heating downstairs from upstairs, worked out problem was apparently upstairs, and found leak 3 months ago. Fixed that. As soon as leak fixed, 2 different radiators, which had previously been pretty warm, lacked heat (both upstairs). Now we are back to almost zero on boiler pressure. We trust the plumbers, they're longstanding reputable large firm, have worked for friends and done a great job for us on other occasions. But this seems to have them stumped. Any ideas...?

"2 different radiators, which had previously been pretty warm, lacked heat"

all your radiators need balancing

"back to almost zero on boiler pressure"
Probably a leak still. Start by looking at the pressure relief valve that comes out of the wall, on the outside of your house, behind the boiler. Are there signs it has been dripping? What is your boiler pressure (a) hot and (b) cold? Do you know how to top it up?

or
www.mumsnet.com/Talk/property/a2205419-New-radiators-not-getting-hot#50023831

Thanks PigletJohn. I will try this. No, we've tried the pressure relief valve countless times and it is fine - no signs of dripping ever, and plumber left a plastic bag on it for a few weeks at one point to check this. We have topped up boiler and bled radiators several times over last year; does raise boiler pressure but then back to zero within a couple of weeks. I diagnosed leak but took a while for plumber to find it. Sounds like either it has opened up or there is another somewhere. They've been all over, but clearly something has been missed.

By no means an expert or indeed a plumber but did have a lengthy convo with our plumber re similar problems with our boiler pressure and lack of heat to some rads. He thought 2 things 1) system needs another expansion point ( can't remember the exact term) and 2) as we have been bleeding and re filling the system frequently the stuff they put in the rads might need topping up ( because plain old water goes stale sbd gives off a gas that fills the rad) . Could be rubbish but worth a thought.

yes, the hot and cold pressure readings will show if there is a problem with the expansion vessel (though they should have checked that).

Corrosion inhibitor should have been added when the new rads were fitted, but yes, frequent bleeding of gas does indicate corrosion.

Some cold rads is usually a balancing problem though.

Sorry I'm slightly hijacking your thread her but Piglet John - if our rads are all hot once they have been bled and the boiler pressure back up but a week later the temp of the 2 rads on the end of the run is down and they are full of air again does that indicate rebalancing or poss more to the 2 ideas our plumber gave us?

balancing first if you have one or more radiators cold or cool all over..

If you have one or more radiators full of air, you probably have a sludge or corrosion problem. You will know if you feel the tops of all the radiators. Radiators that are cold at the top have gas in them. It is also possible for a leak on the suction side of the pump to suck air in, but this is not common with a pressurised system.