Boiler losing pressure? Here’s what it usually is (and how to stop the top-up loop).
If you’ve topped it up, walked away, then checked the gauge the next morning and sighed… yeah. This is that page. I’ve seen people treat it like brushing their teeth: kettle on, pressure up, off to work. It feels “manageable” until it isn’t.
People search “boiler repair near me” and “boiler repairs near me” when this happens because you can’t really ignore it. A sealed system shouldn’t be drinking water. If it is, something is leaking, dumping, or behaving badly when it heats up.
Quick call tip: tell us the gauge reading cold and again after the heating has been on for 30 minutes. That one detail saves a lot of guesswork.
A proper Newham example (the kind you don’t spot from a quick Google)
We were in Newham, not far from Stratford, in one of those older conversions where the pipework has been “edited” over the years. The owner swore the boiler was fine because it fired up every time. But pressure dropped every 24–48 hours.
No puddles. No dramatic leaks. Just that faint chalky staining on a radiator valve upstairs and a bit of damp dust on the tail pipe. When the heating warmed up, it weeped. When it cooled, it stopped. Easy to miss. Easy to live with… until it becomes a bigger issue.
What “losing pressure” actually means
Your heating is (usually) a sealed circuit. The water goes round and round — it’s not meant to disappear. So if pressure drops, one of three things is happening:
1) Water is leaving the system
- Small leak at a radiator valve, joint, or visible pipework
- Boiler components weeping internally (sometimes you’ll see staining underneath)
- Slow loss that evaporates before you notice it
2) It’s dumping when it heats up
- PRV discharging outside after a pressure spike
- Expansion vessel not doing its job, causing big hot/cold swings
3) You topped up once after bleeding… and that was normal
That’s fine. The key word is once. If you’re topping up again and again, it’s not “just because I bled the rads”.
Safe checks you can do without turning it into a mess
I’m not here to pretend you can’t do anything. You can. Just do the sensible bits.
Do this
- Take a photo of the gauge cold, then again when heating has been on for ~30 minutes.
- Run your hand under radiator valves and obvious joints (look for dampness, green crusting, staining).
- Look under the boiler for water marks (torch + a quick glance, not a full dismantle).
- If you have an outside discharge pipe, check for drips or water marks.
If you’re unsure, ring us and describe what you see: 07727 154746.
Don’t do this
- Don’t keep filling it daily “to get through the week”.
- Don’t push pressure high “to be safe”.
- Don’t keep resetting lockouts without figuring out why it’s happening.
- Don’t drain the whole system unless you actually know what you’re doing.
Stop DIY when the risk outweighs the “savings”
If pressure loss is paired with anything that hints at combustion or electrics being involved, that’s the line. The point isn’t to be dramatic — it’s because the downside is ugly.
When it needs a proper boiler repair visit
If pressure drops more than once in a week, or you see big hot/cold swings, or you’re spotting staining but can’t find the exact source — that’s when diagnosis matters. Most of these faults are component-level fixes: PRV, expansion vessel recharge, valve replacement, joint repair.
If you’ve been bouncing between “boiler repair” and “gas boiler repair near me” searches, this is the clean route: arrange a Gas Safe boiler repair inspection.
If you’re in Newham and the boiler’s in a hallway cupboard (typical flat setup) and you can’t risk it failing overnight, call 07727 154746 and tell us the cold + hot gauge readings. That’s usually enough to point us in the right direction before we even arrive.
Related diagnostics (same intent, no overlap)
If pressure loss is happening alongside any of these symptoms, these guides connect the dots properly:
- Radiator cold at the bottom: sludge signs
- Kettling boiler noise: scale vs flow problems
- Radiators not heating upstairs: causes & fixes
Back to the main site: ARA Services homepage.
Boiler losing pressure FAQs
Is it normal for boiler pressure to drop a bit?
A small drop after bleeding radiators can be normal. But if you’re topping up repeatedly, treat it as a fault. A sealed system shouldn’t need regular water.
My pressure rises when heating is on, then drops low later. What’s that?
That hot/cold swing often points to expansion vessel behaviour and/or PRV discharge. It’s commonly repairable. The pattern (cold reading vs hot reading) is the giveaway.
Can I just keep topping it up for now?
You can top up once to restore heating, but repeating it introduces fresh water (and oxygen) which accelerates corrosion. It’s a short-term workaround, not a solution.
Does low pressure mean I need a new boiler?
Not automatically. Pressure loss is often caused by repairable components or small leaks. A targeted repair can stabilise the system and extend the boiler’s life.
What’s the quickest info to tell an engineer on the phone?
Give the gauge reading cold, then again after the heating has been on for 30 minutes, plus whether you’ve noticed any damp patches or staining. That’s usually enough to narrow down likely causes.