Boiler Pressure Too High in Croydon?
What it usually means when the gauge keeps rising, hits 3 bar, or starts dripping outside
If your boiler pressure is too high, the first thing is not to panic, but it should not be ignored either. A sealed heating system normally rises a bit when the heating comes on, but pressure heading towards 2.5–3 bar usually means something needs checking.
In Croydon homes, especially older houses in Thornton Heath, Norbury and West Croydon, we often see this after someone has topped the boiler up, after a missed service, or when the expansion vessel inside the boiler stops absorbing pressure properly.
MPS Heating & Plumbing LTD helps homeowners across Croydon, Thornton Heath, Addiscombe, Norbury, South Croydon, West Croydon, Selhurst and East Croydon with high boiler pressure, pressure relief valve leaks and boiler pressure faults. We have a 5.0 Google rating from 60 reviews.
If your boiler pressure is at 3 bar, water is coming from the outside copper pipe, or the pressure keeps rising after you lower it, call 0203 576 6769 and we’ll talk through what is likely happening before you book.
Why Boiler Pressure Keeps Rising Towards 3 Bar
Most combi and system boilers normally sit somewhere around 1 to 1.5 bar when the heating is cold. Then once the radiators kick in and everything warms up, the pressure usually creeps up a bit. That part’s normal.
It becomes a problem when the gauge keeps climbing and starts heading towards 2.5 or 3 bar, especially if it shoots up fast after you top the system up or turn the heating on. At that point, something usually isn’t behaving properly anymore. Could be the filling loop passing water when it shouldn’t. Could be the expansion vessel losing its charge. Sometimes the pressure relief valve has already opened once and never quite seals properly again, so you end up with that annoying drip outside that people ignore for weeks.
We see it all the time around East Croydon, Thornton Heath and Addiscombe, especially in older houses where the heating system has been added to over the years. New radiator here, extension there, pipework buried under floors from three different decades. The boiler itself is often blamed first, but a lot of the time the issue sits elsewhere in the system.
And honestly, people do tend to keep resetting boilers hoping it settles down on its own. Sometimes it does for a bit. Then the pressure climbs again a few days later and the same thing starts all over.
If the problem showed up after the boiler has gone a few years without a proper check, have a look at our proper boiler servicing checks page as well. Pressure faults are one of those things engineers often catch during servicing before they turn into leaks or breakdowns in the middle of winter.
Common Causes Of Boiler Pressure Being Too High
| Possible cause | What it usually looks like |
|---|---|
| Filling loop left open | The pressure slowly climbs after the boiler has been topped up. There can be occasions one valve is only slightly open, so it creeps up over a few hours. |
| Expansion vessel fault | A very common one. The pressure can sit looking completely normal while the system is cold, then suddenly climb once the heating starts running. On some boilers it creeps up slowly, on others it shoots straight towards 3 bar and starts dumping water outside through the relief pipe. This can also lead to a boiler losing pressure once the system cools down, especially if the pressure relief valve has discharged. |
| Pressure relief valve leaking | You may see water dripping from the small copper pipe outside. Once the valve has opened, dirt or scale can stop it sealing properly again. |
| Internal boiler fault | On some combi boilers, a plate heat exchanger or internal valve issue can let mains pressure affect the heating circuit. |
Why It Often Gets Worse When The Heating Comes On
A slight pressure increase once the heating fires up is completely normal. The water inside the system expands as it gets hotter, so the gauge usually moves a little. Most people never even notice it.
The trouble starts when the boiler has nowhere to absorb that extra pressure anymore. That is usually where the expansion vessel comes in. If it loses its air charge, or sometimes the connecting pipe gets partially blocked with sludge and old system debris, the pressure can rise surprisingly fast once the radiators warm through.
We see boilers sitting calmly at 1.2 bar cold, then 10 minutes later they are nearly touching 3 bar and dripping outside through the copper discharge pipe. Especially in older heating systems around Croydon where bits have been changed over the years but the system itself has never really been cleaned properly.
And to be fair, a lot of homeowners only notice it once the heating has been on for a while in the evening. Everything seems fine during the day, then suddenly there is water outside or the boiler locks itself out overnight.
An engineer will normally watch what the pressure does from cold all the way through a heating cycle. That tells you far more than standing there resetting the boiler three times hoping the gauge magically behaves itself again.
If the pressure climbs quickly, drops once the boiler cools down, then repeats the same pattern the next time the heating comes on, expansion vessel or pressure relief valve checks are usually where the investigation starts.
When It May Be Simple
If somebody has recently topped the boiler up, there is always a chance the system has just been overfilled slightly. Happens more than people think, especially after watching quick online tutorials where nobody explains when to stop filling.
Sometimes the pressure can be reduced safely from a radiator bleed point or drain point, but only if you actually know what you are doing. We still get calls from people who accidentally drop the pressure too low afterwards and end up with the boiler refusing to fire at all.
When It Needs Diagnosis
If the pressure keeps rising after being lowered, that is not just “too much water”. It could be a passing filling loop, expansion vessel issue, PRV fault or internal boiler problem.
When It Is Urgent
If the gauge is at 3 bar, the boiler is leaking, the outside copper pipe is dripping, or the boiler keeps locking out, it is safer to stop guessing and arrange a proper check.
A Common Croydon Callout We See
A customer in a flat near East Croydon had topped the boiler up after seeing low pressure. The heating came back on, so they thought it was sorted. Later that evening the gauge was nearly at 3 bar and water was dripping from the copper pipe outside.
That one turned out to be a filling loop not fully shutting, with the pressure relief valve passing afterwards. The boiler did not need replacing. It needed proper pressure checks, the valve issue dealt with, and the system set back to the right cold pressure.
If you’re in Croydon, Thornton Heath, Norbury or nearby and the pressure keeps rising, call 0203 576 6769. We’ll tell you if it sounds like a simple pressure issue or something that needs a Gas Safe engineer.
No Guesswork
We check how the pressure behaves cold, hot and after the system cools down. That helps separate a simple overfill from an expansion vessel, PRV or internal boiler fault.
Straight Advice
If it only needs the pressure setting correctly, we’ll say that. If a part has failed, we’ll explain what has failed and why before any boiler repair work goes ahead.
Local Experience
We Conduct work on a few different brands which are inclusive of Worcester Bosch, Vaillant, Ideal and Baxi boilers and we aere Gas Safe Registered — ID 662170.
Boiler Pressure Repair Prices In London
High boiler pressure repair costs depend on what is causing the pressure rise. A straightforward filling loop issue may be much less than an internal expansion vessel replacement or plate heat exchanger fault.
As a rough London guide, simple boiler fault checks and minor pressure repairs often sit around £100–£200. Expansion vessel work can commonly range from about £180–£450 depending on access, boiler model and whether the vessel is internal or external. PRV or filling loop repairs are usually priced after inspection because the cause matters.
We explain the likely cost before work starts. No rushed checks, no guessing, and no pushing a new boiler if the pressure fault can be repaired properly.
What Customers Have Said
“Really helpful over the phone and explained what was happening with the boiler pressure before coming out. No nonsense, just clear advice.”
— Croydon customer“The boiler kept going into the red and dripping outside. MPS found the issue quickly and explained the repair properly.”
— Thornton Heath customer“Turned up when they said they would and checked the boiler properly. It was not made into a bigger job than it needed to be.”
— Addiscombe customerNeed Help With High Boiler Pressure?
If you’re in Croydon, East Croydon, Selhurst, South Croydon, Thornton Heath, Addiscombe or Norbury and your boiler pressure is too high, we can help you work out the next sensible step.
When you call, tell us the cold pressure, what it rises to when the heating is on, and whether there is water coming from the outside copper pipe. That usually gives us a good starting point.
Boiler Pressure Too High FAQs
Is 3 bar too high for a boiler?
Yes. Around 3 bar is usually where the pressure relief valve starts opening to protect the system. If your boiler keeps reaching 3 bar, especially when the heating is on, it needs checking rather than repeated resetting.
Why is my boiler pressure too high when the heating is on?
This often points to an expansion vessel issue. As the water heats and expands, the vessel should absorb the pressure rise. If it has lost charge, failed internally, or is blocked off by sludge, the pressure can rise very quickly.
Can I lower boiler pressure myself?
Sometimes, yes, if the system has simply been overfilled. But if the pressure keeps rising again, or you see water outside from the discharge pipe, lowering it will not fix the real fault.
Why is water dripping from the copper pipe outside?
That pipe is usually connected to the boiler pressure relief valve. If it is dripping, the boiler may have over-pressurised or the valve may not be sealing properly after opening.
Should I turn the boiler off if the pressure is too high?
If the pressure is at 3 bar, the boiler is leaking, or it keeps climbing when heating is on, it is sensible to turn the heating off and call for advice. Do not remove the boiler casing or touch gas-side parts.