Boiler Losing Pressure? Common Causes & How to Fix It

Boiler Losing Pressure? Causes

Boiler pressure problems are one of the most common heating issues we attend across East Grinstead, Crawley, Tunbridge Wells and surrounding postcodes.

If your boiler keeps losing pressure, it can cause:

• No heating
• No hot water
• Boiler lockouts
• Constant resetting

Below we explain the most common causes — and when it’s time to call a Gas Safe engineer.

What Should Boiler Pressure Be?

Most modern boilers should sit between:

1.0 – 1.5 bar when cold

If your pressure drops below 1 bar, your boiler may stop working or display a fault code.

If you’re constantly topping it up, that’s a sign something isn’t right.

1. Leaks in the Heating System (Most Common Cause)

The most common reason a boiler loses pressure is a small leak somewhere in the system.

This could be:

• Radiator valves
• Pipework under floors
• Upstairs radiator joints
• Towel rails
• The boiler itself

We regularly trace hidden leaks in homes across Crawley, East Grinstead and surrounding postcodes, especially in older properties.

2. Faulty Expansion Vessel

Inside your boiler is an expansion vessel that absorbs pressure changes as the system heats up.

If it fails:

• Pressure rises when heating is on
• Pressure drops when it cools
• You may see water discharging outside

This is a very common boiler repair across Tunbridge Wells and surrounding postcodes.

3. Pressure Relief Valve (PRV) Issue

If the system has previously over-pressurised, the PRV may have opened.

Sometimes it doesn’t reseat properly, which causes:

• Constant slow pressure loss
• Damp patch near the discharge pipe outside

This usually requires professional repair by a Gas Safe engineer.

4. Older Boiler or Internal Corrosion

In boilers over 10–15 years old, internal corrosion can lead to ongoing pressure problems.

If your boiler is regularly losing pressure and also:

• Making unusual noises
• Breaking down frequently
• Over 10–15 years old

It may be worth considering whether repair or replacement is the better long-term option.

Can You Just Keep Topping It Up?

You can temporarily top up your boiler using the filling loop — but this is not a permanent fix.

Repeated topping up:

• Introduces fresh oxygen into the system
• Accelerates corrosion
• Can damage internal components

If you’re topping up more than once every few months, it’s time to investigate properly.

When to Call a Gas Safe Engineer

You should seek professional help if:

• Pressure drops repeatedly
• The boiler keeps locking out
• You see water under the boiler
• The discharge pipe outside is dripping
• You’re unsure how to safely top it up

Rapid Flow Plumbing & Heating provides boiler repairs and fault diagnosis across:

• East Grinstead
• Crawley
• Tunbridge Wells
• Surrounding postcodes

Boiler Repair in East Grinstead & Crawley

If your boiler is losing pressure, we’re happy to help.

Call: 07775 976 278
Email: rapidflowheating@gmail.com

We provide professional boiler repairs, heating diagnostics and fault finding across East Grinstead, Crawley and surrounding areas.

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