BoilerFaultCodesBoiler guides & tips
Plain English answers to common boiler problems, buying decisions, and maintenance. Written for UK homeowners — no technical knowledge needed.
When something's wrong
Boiler leaking water?
Turn it off and stop the water first. Then use where the leak is coming from to work out what failed and what it costs.
What pressure should my boiler be?
Cold, 1 to 1.5 bar. The figures quoted from Worcester and Ideal manuals, and what to do when yours is outside the range.
Thermostat not working?
Start with the batteries, even if the screen looks fine. Includes the quirks of Honeywell, Hive, Nest, Salus, Worcester and Vaillant.
Radiator valve not working?
Valves seize shut over summer. Find the pin under the head and free it in two minutes, for nothing.
How to bleed a radiator
Two minutes per radiator, and the tool costs a pound. Includes what to do without a key, and the pressure check most guides skip.
Radiator not heating up?
One cold radiator and one cold house are different faults. Count the cold ones first, then follow the right set of checks.
Hot water works but the heating doesn't
If the taps run hot, the boiler is fine. It's the part that decides where the heat goes. Usually a diverter or motorised valve.
Boiler pressure too high?
What the gauge should read cold, why it climbs, and how to bring it down yourself with a radiator key.
Frozen condensate pipe: fix it in 10 minutes
The most common winter boiler fault — and one you can safely fix yourself without an engineer.
Low boiler pressure: how to repressurise
Step-by-step guide to using the filling loop to top up your boiler pressure safely.
Why does my boiler keep losing pressure?
You top up and it drops again within days — here are the six most common causes, ranked.
Banging, kettling or whistling noise
Each noise points to a different problem. Here's how to tell what yours means and how urgent it is.
No hot water but heating works
On a combi boiler, this is almost always a stuck diverter valve. Here's how to confirm and the fix cost.
Boiler won't turn on: full checklist
Nine checks to work through before paying £85 for a call-out. 40% of "won't fire" calls are fixable in 10 minutes.
Boiler keeps cutting out or locking out
Fires up then shuts down with a fault code. The six causes we see most often in the fault data.
Pilot light keeps going out
Older boilers only — here's why the pilot won't stay lit and whether it's worth repairing.
Radiators cold at the bottom
Top hot, bottom cold = sludge build-up. Bleeding won't fix it. Here's what does, and what it costs.
Yellow or orange flame — safety critical
A yellow flame can mean carbon monoxide risk. Turn the boiler off first, then read this.
Repair, replace, or upgrade?
Gas safety certificate (CP12)
About 30 minutes and £60 to £100 for one boiler. Who legally needs one, what gets checked, and how it differs from a service.
Boiler service cost in 2026
What you should pay, what a proper service actually includes, and the signs you only got a ten-minute look.
When to replace your boiler: 7 signs
Repair or replace? Here's a simple calculation for whether a new boiler actually saves you money.
How much does a new boiler cost in 2026?
Realistic UK prices by boiler type. What adds cost, what you can skip, where quotes vary most.
Best combi boiler 2026 UK
Honest picks by category — best overall, best value, best premium — based on fault-code data across 17,000 boilers.
Worcester vs Vaillant vs Ideal
Honest comparison of the UK's three biggest brands. No installer commission bias.
Boiler finance explained
0% APR vs buy-now-pay-later vs extended finance — what they actually cost and when to pay cash.
Heat pump vs new gas boiler
With the 2035 ban coming and a £7,500 grant on offer, is it time to switch? The honest cost breakdown.
Is boiler cover worth it?
Sometimes yes, sometimes a straight waste. Here's how to tell which camp you're in — with a break-even calc.
Start here if you're new
Not sure what's wrong?
Use our symptom checker to describe what your boiler is doing — no fault code needed.