📊 What is Normal Boiler Pressure?
Your boiler's pressure gauge shows the water pressure inside the central heating system. The correct pressure for most boilers is:
| State | Normal Pressure | Action Needed |
|---|---|---|
| Cold system (heating off) | 1.0 – 1.5 bar | None |
| Hot system (heating on) | 1.5 – 2.0 bar | None |
| Too low | Below 1.0 bar | Repressurise |
| Too high | Above 2.5 bar | Bleed radiators |
| Dangerously high | Above 3.0 bar | Call engineer |
🔧 How to Repressurise Your Boiler — Step by Step
You will need: A filling loop (usually a flexible silver hose under the boiler) and access to the pressure gauge.
- Turn the boiler off and let the system cool for at least 10 minutes
- Find the filling loop — usually a silver braided hose with two valves under or beside the boiler
- Open both valves slowly — you'll hear water entering the system
- Watch the pressure gauge — stop when it reaches 1.2 bar
- Close both valves tightly
- Turn the boiler back on and press reset if needed
- Check the pressure after the system heats up — it should rise to 1.5-2.0 bar
Do not pressurise above 1.5 bar when cold. The pressure will rise when the system heats up. Over-pressurising can damage the pressure relief valve.
🔍 Why Does Boiler Pressure Keep Dropping?
If you have to repressurise your boiler more than once every few months, there is an underlying problem:
| Cause | Signs | Fix |
|---|---|---|
| Small leak in system | Damp patches near radiators or pipes | Find and fix leak |
| Leaking radiator valve | Drip at radiator base | Replace valve |
| Faulty pressure relief valve | Water dripping from pipe outside | Replace PRV |
| Failed expansion vessel | Pressure rises then drops quickly | Re-pressurise vessel |
| Heat exchanger pinhole leak | No visible leak but pressure drops | Engineer required |
FE Maintenance will find the source of your pressure loss and fix it permanently. We use dye testing to locate hidden leaks. Call 020 8445 1303.
Frequently Asked Questions
You should rarely need to repressurise your boiler — perhaps once or twice a year at most. If you're topping it up monthly or more frequently, you have a leak or expansion vessel fault that needs a Gas Safe engineer to fix properly.
Pressure shouldn't drop significantly overnight. If it does, you have a leak somewhere in the system — possibly a tiny pinhole in a pipe, radiator valve, or the heat exchanger itself. Call FE Maintenance on 020 8445 1303 for a leak investigation.
Yes — pressure above 3 bar can activate the pressure relief valve (causing water to drip outside) and can stress the heat exchanger. If your boiler pressure is consistently high, bleed your radiators and call an engineer if it doesn't come down.
The filling loop is usually a flexible silver braided hose located under the boiler, often in a cupboard. Some modern boilers have an internal filling loop accessed by a lever or key. If you can't find it, call FE Maintenance and we'll guide you over the phone.
If the pressure is correct but the boiler still won't fire, the problem is elsewhere — thermostat, ignition, gas valve, PCB or another component. Call FE Maintenance on 020 8445 1303 for a same-day diagnosis and repair.
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