Combi boiler - pressure query

My son has just moved into a flat which has a boiler which I presume from his reports is a combi - no storage tank AFAIAA. There is a pressure gauge which is currently reading well into the red. Apparently the heating and probably the hot water are switched off. Is this a problem, how could he release some pressure if necessary and is there any danger in turning it all on? Sorry if these are basic questions but I have only ever had stored water systems myself. TIA.
Peter.
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"PJK" wrote...

Hi Peter, if the flat has been empty for a while (the college / Uni Xmas break, for instance), it's more likely the red's at the low pressure end (showing less than 1 bar or so) - if so, neither heat nor water should be used until it's repressurised - the hot water might work anyway, though.
Under the boiler there'll be a pipe from the rising main with a fill valve (similar to an isolator valve, with an open threaded end and either a screw-slot or a lever) and a filling loop (a flexible pipe with a matching threaded end) connected to a one-way valve into the heating circuit - at least the filling loop's open end *shouldn't*be connected if the water reg's are being followed, usually they are as they're often in an inaccessible spot!
To correct the pressure, attach the filling loop to the fill valve (fairly tightly) and open the fill valve, observing the reading on the gauge and closing the valve once it's somewhere in the middle. Your son may need to repeat this procedure once the heating's running if he notices cold tops to the radiators and has to bleed the air out to get them working properly.
To bleed the radiators he'll need a radiator bleed key (surprise!) from the DIY shed, a couple of quid, to open the bleed valve at one end of the top of the radiator a couple of turns until he can hear air hissing from the valve, and a rag to catch the drips and/or spray of filthy radiator water before it gets on the landlord's carpet / wallpaper / curtains - close the bleed valve once water flows. Once the radiators are bled, check the gauge reading, top up if required, repeat the procedure if (when) the pressure drops again.
Hope that helps, Dave H. (The engineer formerly known as Homeless)
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...

...
Bleed a radiator or let the pressure relief valve take care of it. The only problem in having the heating or hot water 'switched off' is that you won't get any heating or hot water ;-) Oh and a severe frost may make your pipes holey. Depends what you mean by switched off. - boiler off electrically, room thermostat too low, airlock in boiler, bolier DHW thermostat off or too low, same for heating.....
--
Mike W



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PJK wrote:

Probably best to relieve the pressure. Easiest way is if there are any draining points anywhere on the central heating (normally by radiators and/or at the lowest point on the system - just unscrew the valve on the drain point and drain off enough to bring the pressure down to the green or blue zone. Shouldn't need much liquid removing at all; if the pressure doesn't fall, this might mean that the central heating is hooked up to the water main and the valve is open (ie the CH is at mains pressure). In that case, you'd need to locate the filling loop (usually a braided steel hose below the boiler) and turn off the valve at the end.
If there's no drain points there ought to be one within the boiler, or he could loosen off a pipe feeding a radiator slightly - however that's potentially messy - high risk of black sludge on the carpet!
Once he's brought the pressure down, the next thing is to find out whether it stays stable when the system is switched on, or goes up again... that's another (different) question!
David
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On Wed, 31 Jan 2007 19:10:48 +0000, PJK wrote:

Please see the Sealed CH FAQ below.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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Ed Sirett wrote:

many thanks, very helpful. Thanks to all other responders also.
Peter.
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Well depends on the boiler there is many ways, Firstly why is the gauge in the red? is the filling loop still open or passing or did you over fill it? Well back to your question about releasing the pressure it is proberbly best to put a hose on a drain point and release it that way or let it out a bleed valve on a rad, This will take a while and can be a little awkward to do .hope this will give you a start
pete
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