Boiler Losing Pressure? What to Check First
Constantly topping up your boiler pressure? Discover the common causes and when you need to call a Gas Safe engineer.
Waking up to a cold house because your boiler has locked out with a "low pressure" fault code is incredibly frustrating. If you find yourself constantly using the filling loop to top it up, you have an underlying issue.
What's Causing the Issue?
A sealed heating system shouldn't lose pressure. If it drops, the water is escaping somewhere. The two most common culprits are a small leak in the pipework/radiators, or a faulty component inside the boiler itself (like a blown expansion vessel or a leaking pressure relief valve).
What You Can Do Right Now
- 1. Check for visible leaks: Inspect the valves at the bottom of every radiator in your house for damp patches or weeping water.
- 2. Look outside: Check the small copper pipe sticking out of the wall behind your boiler (the PRV discharge). If it's dripping water, the boiler is venting pressure.
- 3. Repressurise (temporarily): Use the filling loop to bring the pressure back to 1.5 bar so you have heating, but know this is a temporary fix.
When It Becomes Serious
Constantly introducing fresh, un-treated water into your heating system dilutes the protective inhibitor chemicals. This causes the inside of your radiators to rust rapidly, creating sludge that will eventually destroy your boiler's pump and heat exchanger.
When to Call an Engineer
If there are no visible leaks on the radiators and the pressure drops within a few days of topping up, you need a Gas Safe engineer to diagnose the boiler's internal components.
Boiler Diagnostics in Newport
Our engineers regularly attend pressure loss faults across Newport and Cwmbran. We carry the testing equipment needed to check expansion vessels and PRVs safely. Get help from our Newport team.
Frequently Asked Questions
What should my boiler pressure be?
When the system is cold, the gauge should read between 1.0 and 1.5 bar. It's normal for it to rise slightly when the heating is on.
Can low pressure be dangerous?
No, modern boilers have safety switches that shut them down if the pressure drops too low, preventing them from firing dry and causing damage.