Assuming the filler loop is disconnected, then the expansion vessel has lost it's charge or duff.

Disconnect it then and check if it's letting by

He means allowing water to pass through. If you disconnect the flexible hose bit, no water should emerge other than the water already present in hose.

if its not the filling loop, check the expansion vessel, they are usually re-charged with a hand pump, like the one you blow up bike tyres with.


btk

I have removed filler loop and there is no water other than that which was in the tube so it is letting by, where do I find the expansion vessel ? when I put the heating on the dial goes up two bar, is this dangerous ? I have been told its not and that the pressure will be released via the valve and overflow

yes please also how do I pump it up if thats what is needed

If the system pressure is continuously increasing, there must be mains pressure water entering. If it's not via the filling loop, it might be via a leak in the secondary heat exchanger.

If you are sure it's NOT the expansion vessel or filler then...

I've just been through a similar problem. In our case the pressure of the mains coming into the house increased to 5 bar and that caused the 3 bar relief valve on the boiler input to open. The first we knew about it was a £700 water bill.

To confirm the problem add a pressure guage to the mains input to the house.

The solution in our case was to fit an adjustable (1-4 bar) pressure regulator just before the boiler relief valve. Set it to say 2.75 bar. It helps if you add a second pressure gauge after the regulator so that you can adjust it accuratly.

This cured the problem for us but introduced a minor irritation... The pressure regulator isn't a very good regulator. Sure it always stops the pressure exceeding the set value BUT it also reduces the flow rate when the taps are on. With the hot taps off the pressure is the set value (eg 2.75 bar) but as soon as you open a tap it falls to 0.75 bar. The new regulator is clearly the problem because we didn't have this problem before fitting it. I've tried two different makes with little real improvement.

PS Any flow through the filler will increase the pressure. Be really sure that it's not allowing drips through. Let the filler pipe drain into a bucket overnight and see if it's still dripping the following day.