Boiler is in daughter's house. System has 7 single panel radiators.
With the cold pressure on 1.2 bar, it rises pretty quickly to about 2.5 bar when hot.
I found my neighbour has exactly the same boiler and that barely moves - a couple of tenths of a bar.
Is the pressure rise anything to be concerned about, and is there a logical reason why they would they be so different?
Most likely a failing (or failed) expansion vessel. If it is built into the boiler it's usually a lot cheaper and easier to add a new external expansion vessel than to replace the original.
The installation manual for your boiler should contain details on how to check the pressure of the expansion vessel. If water comes out of the schrader valve it's a sign that the diaphragm has failed.
Tim
The service booklet for this boiler is available online.
It says (for expansion vessel replacement):
Drain the central heating circuit as described in Section 16.3, a. Hinge the facia panel into the servicing position as described in Section 15.3, c. Remove the air pressure switch, gas to water heat exchanger, water to water heat exchanger and pump as described in 16.4, 2, 5,
14 and 20 and remove the vessel. Fit the replacement vessel in the reverse order.As you say, fit an external one if it's not too unsightly. :)
Well 2.5 bar is not too high and is within the allowable range. However its quite a large rise for a system that does not sound like it has a huge water content. Hence as others have suggested, it may indicate a lack of charge in the pressure vessel.
Assuming it has not actually ruptured, it may just need a top up. To do this you need to turn off the boiler and let the system cool, then bleed a couple of litres of water out of the system somewhere (from a rad connection say) to relieve the pressure in the system.
Then (if you can get to it) there should be a shrader valve (like on a car tyre) on the expansion vessel. Test that with a pressure gauge, and if its low (i.e. less than say 2 bar) pump it up with a normal tyre pump, to whatever is recommended in the manual (probably over 2 bar)
If when you test the valve pressure, waster comes out, then you know the vessel is knackered.
Thanks - I thought that if the vessel had failed then the pressure would sh oot up over 3 bar and water would be ejected? I'm pretty sure there no rad full of air to absorb the increase either.
I checked the pressure vessel with the water pressure out of the system and it's 9psi - the manual says it's set at 0.5 bar initially although there's a table (9) in the manual that doesn't makes sense to me (I can't tell wh ich is the pressure vessel setting and which is the water presure setting).
Are you *sure*? If you charge it to 2 bar or more, it won't do anything until the system pressure exceeds that. I always reckon to charge it to about 10psi (about 0.7 bar). Then, if the cold water pressure is set to (say) 1 bar, the expansion vessel provides a bit of resilience, and allows you to bleed the radiators.
[Are you sure you're not thinking of the vessel for a non-vented HW system?]
In fact I might be thinking of my unvented DHW one rather than the boiler... however go by what the manual suggests.
Yes, quite possibly ;-)
If it had failed completely, then yes. If however its just lost pressure, then the normal "cold" pressure of the system may be taking up most of the expansion room in the vessel.
(note see my reply to Roger, I think he is correct - I over stated the "relaxed" pressure)
Yup that seems reasonable.
WRT the neighbour's system, they may have a rad full of air. Also are they running lower flow temperatures than you?
To be fair, the default setting is normally fine unless you have a particularly large water content system.
It's obviously a possibility that there's air in one or more of my neighbour's rads. I did notice the CH was set a bit lower on the boiler too, although the house was comfortably warm.
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