Boiler Losing Pressure Overnight in Orpington or Bromley? Here’s What’s Really Happening
You top it up to 1.3 bar before bed. Everything looks fine. By morning? It’s dropped again. That pattern — pressure falling while the heating is off — usually points to something specific.
Why It Happens When The Heating Is Off
When the system cools down, the water contracts. That’s normal physics.
But when there’s a weakness somewhere — a tired expansion vessel, a small leak, or a pressure relief valve that isn’t sealing properly — the cooling cycle exposes it.
Around Orpington and Bromley, I see this most in systems 8–15 years old. Not ancient. Just at that “components starting to age” stage.
Expansion Vessel Explained Simply
Inside your boiler (or mounted nearby) is a small tank with a rubber diaphragm. One side is air. The other side is system water.
As water heats and expands, the vessel absorbs the pressure increase. When it cools, it stabilises the system.
If that vessel loses air charge or the diaphragm fails, pressure spikes when hot… then drops when cold. That’s the classic overnight pressure drop pattern.
Pressure Relief Valve Problems
Another common cause is the PRV (pressure relief valve).
If pressure previously rose above 3 bar, the valve opens to protect the system. Sometimes, especially in hard water areas like BR6, it doesn’t reseal perfectly.
Result? Slow discharge outside via the copper pipe — and pressure dropping quietly overnight.
What This Usually Means (And What It Doesn’t)
It rarely means “you need a new boiler.”
More often, it’s:
- Expansion vessel recharge
- Vessel replacement
- PRV replacement
- Small system leak repair
If ignored, repeated pressure loss can eventually lead to total heating failure.
If your pressure is simply low all the time (not just overnight), that’s slightly different — start here: boiler pressure below 1 bar guide.
Common Pattern I See in Local Homes
In 1930s semis around Petts Wood or terrace homes near Bromley North, I often see older radiators paired with newer boilers.
The boiler is fine — but the system’s expansion control isn’t. After a few winters, the pressure cycle starts misbehaving.
About SKR Plumbing & Heating
I’m Stuart — sole trader covering Orpington and Bromley. You can check independent feedback here: Checkatrade reviews.
I work 24/7. If I’m on a job, I’ll call back as soon as I’m free.
Overnight Pressure Drop FAQ
Is it safe to keep topping it up daily?
No. Repeated filling introduces fresh oxygen, which can accelerate corrosion.
Can weather cause pressure loss?
Cold weather affects contraction slightly, but it shouldn’t cause ongoing loss unless something else is weak.
How long does diagnosis take?
Most pressure-related faults can be narrowed down within a standard visit.
Do you cover Bromley as well?
Yes — BR1 to BR6 daily. Call 07706 889 614.
Pressure Dropping Every Morning?
If you're tired of watching the gauge fall overnight, let’s fix the root cause — not just top it up.
Call 24/7 – 07706 889 614