BoilerTroubleshooting2026-02-26
Combi Boiler Low Pressure: How to Fix
Low pressure means topping up via the filling loop — but recurring loss signals a leak.
Low combi pressure causes no-heat lockouts. Topping up is easy, but recurring loss needs investigating.
How to top up
Open the filling-loop valves until the gauge reads 1–1.5 bar (cold), then close them. Reset the boiler if it locked out.
If it keeps dropping
Repeated pressure loss means a leak, a leaking relief valve, or a waterlogged expansion vessel — all needing a technician.
Key takeaways
- Top up to 1–1.5 bar cold
- Use the filling loop
- Recurring loss = a leak to find
- Don't over-pressurize
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