What a falling reading can mean
Loss of water from the heating system can reduce pressure. Possible categories include a visible leak at a radiator or pipe, a hidden system leak, or a fault within the boiler. Pressure can also change after water has been released from a radiator. None of these can be confirmed from a reading alone.
Vaillant’s pressure-loss guidance explains these possible causes and warns against removing the boiler casing. A boiler may stop operating when pressure is outside its permitted range; that does not identify which component needs repair.
Observe without opening or adjusting anything
If the front display is dry and safely accessible, write down the pressure reading and any fault code exactly as shown. Note whether the system was hot or cold, when you noticed the change and whether it has happened before.
From a safe position, look for existing damp marks around accessible radiators or visible pipework. Do not remove covers, tighten joints or reach under a leaking boiler. If water is near electrics, keep clear and seek professional help.
Use the user manual for the precise make and model. There is no single pressure target or filling procedure that suits every system. This guide does not instruct you to operate filling valves or release water; if you are unsure what a control does, leave it alone.
When to call
Arrange help if pressure repeatedly falls, the gauge shows an unexpected change, there is visible leaking or heating and hot water have stopped. Tell John about any recent work or previous topping up, without carrying out another adjustment to test the problem.
For boiler fault-finding and repair, call John on 07973 344480. Have your location, boiler make and model, reading, fault code and the symptoms ready. Explain whether both heating and hot water are affected; the no-heating or hot-water guide helps you describe that distinction.
Use the gas emergency route when needed
If you smell gas, call the National Gas Emergency Service on 0800 111 999 first. John is not a substitute for that service.
For a repair enquiry, John takes calls 24/7 and discusses attendance according to availability. Likely cost is discussed by phone where possible; parts and additional work are discussed before proceeding.