Worcester 28 Si Mk2 Combi Boiler

Help please.
Pressure gauge settles at 3.5 bar when system has been run and switched off. Everything seems fine when boiler is running. Have fitted new filling loop. Still same problem. Any suggestions guys?
Thanks
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off.
loop.
If you are not constantly adding water:
1. Knackered gauge. 2. Filling loop not disconnected. (You should remove the hose after use). 3. Leak in internal heat exchanger that lets mains water into the system.
If you are constantly adding water:
4. Failed/inadequete expansion vessel.
I suspect (3), which is unfortunately a very expensive repair/new boiler situation.
Christian.
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Gino, are you saying the pressure is 3.5 bar hot? If I assume that the pressure drops to <1 bar when cold you may be looking at a lack of pre-charge pressure in the boiler expansion vessel. This will be the case if this condition has crept up on you over several months. If, however, this has been consistently the case from new then you must look at the total water volume in your heating system, and refer to reference books for the required expansion vessel size. The Worcester comes with an 8 litre vessel as standard, so if you have, typically, 15 radiators you may have to add an extra 18 litre vessel. You should check the safety discharge vessel is not dripping as this will cause the pressure to drop.
NOW A WARNING ! Only CORGI registered fitters are legally allowed to work on gas boilers.
Note: the safety valve is set to blow at 3 bar, at an indicated 3.5 bar it is very close to blowing (even allowing for gauge error), so don't work on a hot boiler.
Good luck....PJ

off.
loop.
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