Boiler breakdown: what to do
Save £100–300 in 30 mins — no heating engineer needed
Most people call a heating engineer for this. You probably don't need to.
Last updated: March 2025
Only basic tools needed — most homes already have them.
Before you start
Many boiler "breakdowns" can be resolved without an engineer. Low pressure, a tripped thermostat, a frozen condensate pipe, or a simple reset fix the problem in around 30% of callouts.
Never attempt to work on the gas supply itself. If you smell gas, leave the building immediately, call the National Gas Emergency Service on 0800 111 999, and do not return until they have given the all-clear.
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Tools & materials
- ✓Nothing needed— diagnosis requires eyes and the boiler manual
- ✓Boiler manual— find your model online if you don't have the original
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Check the basics first
Is the boiler switched on? Is the room thermostat set high enough? Is the programmer set to heating mode? Are the gas supply and electricity supply on? These seem obvious but are responsible for a surprising number of "breakdowns".
Most people get this done in under 5 minutes.
Where beginners go wrong
Repeatedly pressing reset without diagnosing — a boiler that locks out exists for a reason. Clearing the lockout without fixing the cause just delays the breakdown.
Calling an engineer without noting the error code — a precise code allows an engineer to come prepared and saves a repeat visit.
Ignoring a boiler that works but cycles on and off frequently — this is a warning sign of a heat exchanger or pump issue that will escalate.
Emergency: call 0800 111 999 if...
You smell gas — leave immediately, do not use light switches or phones inside
You suspect carbon monoxide — symptoms: headache, dizziness, nausea — leave immediately and call 999
Your carbon monoxide alarm sounds
Typical repair costs
Recommended starter kit
Five tools that cover most home repairs.
- →Adjustable spannerAmazon·Screwfix
- →Screwdriver setAmazon·Screwfix
- →PTFE tapeAmazon·Screwfix
- →Spirit levelAmazon·Screwfix
- →Tape measureAmazon·Screwfix
Want everything in one go? Get it on Amazon
What you just learned
You now know how to systematically diagnose a boiler fault and distinguish between what you can fix yourself and what needs a Gas Safe engineer. A prepared diagnosis saves time and money on every callout.
Most people would pay a tradesperson for this.
⚠️ Watch out if you rent
A broken boiler in winter is an emergency. Landlords must fix heating and hot water within 24 hours in cold weather. Contact them immediately in writing and if they do not act, contact your local council Environmental Health team.