Why Does My Boiler Keep Losing Pressure?
If you are constantly topping up boiler pressure, there is usually an underlying reason worth finding rather than treating the pressure gauge as the problem.
Key takeaways
- Occasional small pressure changes can be normal, but repeated pressure loss needs a cause.
- Leaks can be inside the boiler or elsewhere in the heating system.
- Expansion-vessel or pressure-relief-valve problems can also cause pressure to fall.
- Repeatedly topping up the system can mask the fault and introduce fresh oxygenated water.
What pressure should a boiler show?
Many sealed domestic heating systems operate around the 1 to 1.5 bar region when cold, but the correct range varies by appliance and system. The boiler manual is the right reference. Pressure naturally rises as the heating warms and falls again as it cools.
Check for visible leaks first
Look around accessible radiators, valves and visible pipework for dampness or staining. A tiny leak can lose enough water over time to lower system pressure without creating a dramatic puddle. Do not remove the boiler casing to search for internal leaks.
Expansion-vessel problems
The expansion vessel absorbs the increase in water volume as the system heats. If it has lost charge or failed, pressure can climb excessively when hot and then fall very low when the system cools. That pattern is useful information for an engineer.
Pressure-relief valve discharge
If system pressure rises too high, a safety valve can discharge water. Once a valve has opened, debris or wear can sometimes prevent it resealing perfectly. An engineer can test the cause rather than simply replacing parts by guesswork.
Should you keep repressurising the boiler?
Follow the manufacturer instructions if you know how to top up the system safely, but repeated topping up is not a long-term fix. Fresh water adds oxygen and can contribute to corrosion. If pressure keeps falling, the source should be investigated.
What this means for local homes.
Repeated pressure loss is a common reason homeowners across Mid Sussex contact us. The useful information is the pattern: how quickly pressure falls, whether it rises sharply when hot, whether any radiator valves or pipework are damp, and whether water appears outside from a discharge pipe.
Infinite Plumbing & Heating is based in Lindfield, Haywards Heath, and works across Lindfield, Cuckfield, Newick, Henfield, Heathfield and Burgess Hill, with selected work in Brighton and surrounding areas. If you want advice on a specific property, send the postcode and system details so the next conversation starts with useful context.
Frequently asked questions
Can a radiator leak make boiler pressure drop?
Yes. Any water loss from a sealed heating circuit can lower pressure.
Why does pressure rise when the heating is on?
Water expands as it heats, so a rise is normal. A very large rise can point to an expansion-related problem.
Is low boiler pressure dangerous?
Low pressure normally causes operational problems or a boiler lockout rather than a gas leak, but the underlying cause should still be found.
When should I call an engineer?
If pressure repeatedly falls, rises unusually high, the boiler discharges water or you cannot safely repressurise it according to the manufacturer instructions, arrange professional diagnosis.
Need advice on your own system?
Online guidance can narrow the possibilities, but the right answer depends on the property and equipment in front of you. Call 07765 006759 or send an enquiry and we’ll help with the next step.
