Why Your Boiler Pressure Keeps Dropping (and What to Do About It)
Cambridge mornings can feel extra cold when your boiler decides to play up. You check the gauge, it’s dropped again, and the heating won’t kick in. Sound familiar? Low boiler pressure is one of the most common heating niggles we see across the city. The good news is that it’s usually easy to diagnose and fix once you know what’s going on.
What Boiler Pressure Actually Does
Your boiler pressure helps push hot water around your central heating system. Too little and the radiators won’t heat properly. Too much and the system can overwork or even trip a safety cut-off.
Most boilers in Cambridge homes should sit between 1 and 1.5 bar when cold. You can check the pressure on the gauge at the front of your boiler. If it keeps slipping below 1 bar, you’ve got a problem that needs attention.
Common Reasons for Boiler Pressure Loss
1. Small Leaks in the System
Tiny leaks are the biggest culprit. They can appear in radiators, valves or joints and lose water slowly enough that you don’t see a puddle. Over time the pressure falls and the boiler locks out. Look for tell-tale green or white staining on fittings – a sign of dried antifreeze or inhibitor residue.
2. Leaking Radiator Valves
Older valves and thermostatic heads can weep slightly around the spindle or connection point. It doesn’t look dramatic, but it’s enough to drop the pressure every few weeks.
3. Faulty Pressure Relief Valve (PRV)
The PRV is designed to vent water if pressure gets too high. Once it’s been triggered, grit or limescale can stop it sealing properly. A slow drip from the copper pipe outside the house is a giveaway that it’s passing water constantly.
4. Expansion Vessel Issues
Inside your boiler is a small tank with a rubber bladder that absorbs pressure changes. If the vessel loses its air charge, the system can’t stabilise. You’ll see big pressure swings – high when the heating’s on, low when it cools.
5. Recent Bleeding of Radiators
Bleeding air out of radiators releases pressure too. Always top the system back up afterwards using the filling loop beneath your boiler.
Cambridge-Specific Factors
Our local water is famously hard. Limescale builds up inside boilers, especially older models in areas like Chesterton, Trumpington and Arbury. It can cause valves to stick and seals to fail – both of which lead to pressure loss. Older housing stock doesn’t help either; many properties still have original copper pipework that’s prone to weeping joints and corrosion.
What You Can Safely Do Yourself
- Check the gauge: Make sure the reading is below 1.5 bar before topping up.
- Repressurise carefully: Use the filling loop as shown in your boiler manual to bring the pressure to around 1.2 bar, then close the valves.
- Inspect for drips: Look beneath the boiler, along visible pipes, and under radiators for any signs of moisture.
- Bleed radiators after refilling: A small amount of trapped air can make pressure drop again once released.
If pressure keeps dropping every few days, stop topping up and call a Gas Safe engineer. Constant refilling can pull fresh oxygen into the system, which speeds up corrosion.
When to Call the Professionals
If you’ve checked for leaks and topped up more than twice in a month, something isn’t right. A Plumbox Cambridge engineer can:
- Test the expansion vessel and recharge it if needed
- Replace a faulty pressure relief valve
- Trace and repair hidden leaks
- Clean and repressurise the system safely
In some cases, we recommend a powerflush to clear out magnetite sludge that clogs valves and pressure sensors. It’s a simple fix that can make your system run like new again.
Preventing Future Pressure Problems
Once your system’s healthy, the easiest way to avoid pressure issues is with an annual boiler service or one of our boiler care plans. Regular checks keep seals tight, expansion vessels balanced, and minor leaks caught early.
For more information on maintaining an efficient heating system, visit the Energy Saving Trust for tips on efficiency and energy savings.
In Short
Boiler pressure loss isn’t something to ignore. It’s often a small issue that turns into a big one if left unchecked. Whether you’re in a Victorian terrace near Mill Road or a new build in Eddington, our local boiler engineers can get your system back to full strength quickly and safely.
Book a boiler check today and keep your Cambridge home warm, quiet and running efficiently all year round.
