Hi , Ive got a vaillant combi boiler & the preesure is reading over 3 bar on the gauge.does anybody know how to reduce this as there is water running out of the overflow.
Turn off the valve on the filling system! VERY silly to leave it open!
If this was not the cause, there's a 95% chance you have a leak from the hot water system into the CH system via the secondary heat exchanger in the boiler. (This is unusual fault on Vaillant.) To test this, turn off the cold water supply to the boiler (valve underneath) and let some water out of the bleed screw on a radiator. If pressure gradually drops, you've found the cause. Fix: new secondary HX.
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