Your boiler has packed up. The radiators are cold, the hot tap runs lukewarm at best, and you've got an unhelpful error code blinking at you. Before you call out a plumber at emergency call-out rates, run through these seven checks — about half of all boiler "breakdowns" we get called to in Hertfordshire turn out to be one of the items on this list.
1. Check the boiler pressure
This is the single most common cause of a boiler refusing to fire. Look at the pressure gauge on the front of your boiler — it should read between 1.0 and 1.5 bar when the system is cold.
- Below 0.5 bar: the boiler will lock out for safety. You can re-pressurise the system using the filling loop (the two valves under the boiler, usually with a flexible silver hose between them). Slowly open both valves until the gauge reads 1.2 bar, then close them tightly. Reset the boiler.
- Above 2.5 bar: there's too much water in the system. Bleed a radiator slightly until the pressure drops to 1.5 bar. Don't ignore high pressure — it puts strain on the boiler seals.
If pressure keeps dropping after you re-fill it, you have a leak somewhere in the system — that's when to call us.
2. Check the thermostat and timer
It sounds silly but it catches a lot of people:
- Is the thermostat actually calling for heat? (Set it 5°C above the room temperature)
- Did the timer get knocked into "off" mode or a different schedule?
- After a power cut, smart thermostats sometimes lose their schedule and default to "off"
- If you have a wireless thermostat, the batteries may have died
Replace thermostat batteries every 12 months as a habit — it's the single most preventable cause of "no heat" call-outs.
3. Check the gas supply
If the cooker doesn't light either, you've got a gas supply problem — not a boiler problem. Possibilities:
- You've run out of credit (if you're on a prepayment meter)
- The gas valve in your meter cupboard is closed (someone may have turned it off)
- There's an issue with the gas supply to the property — call your gas supplier's emergency line on 0800 111 999
If you smell gas at any point, leave the property, open windows from outside, and call the emergency line. Do not turn switches on or off.
4. Reset the boiler — properly
Most boilers have a reset button. The trick is that pressing it three times in quick succession will permanently lock out some boilers for safety, requiring an engineer visit to clear.
The correct sequence:
- Press the reset button once and wait 90 seconds
- If the boiler fires up and runs normally, you're done
- If it locks out again immediately, don't keep pressing reset — there's an underlying fault that needs diagnosing
Repeated resets are a sign of a real problem: a faulty fan, a pressure sensor, a flame failure, or a blocked condensate trap.
5. Check the condensate pipe (especially in winter)
Modern condensing boilers produce slightly acidic water as a by-product, drained through a thin white plastic pipe that usually exits the house and goes into a drain. In freezing weather, this pipe can freeze — and your boiler will lock out with a fault code (typically F22, F28 or "EA" depending on the brand).
If it's been below freezing and your boiler has stopped, look for the condensate pipe outside:
- Pour warm (not boiling) water over the pipe to thaw it
- Once thawed, reset the boiler — it should fire up normally
- Consider lagging the external section of the pipe with foam insulation for next winter
If your condensate pipe runs externally and you live in Hertfordshire, this is the single most common cause of "no heat" calls during a cold snap. Worth knowing where it is before winter hits.
6. Bleed the radiators
If some radiators are warm at the bottom but cold at the top, there's air in the system. This won't usually stop a boiler firing, but it will make your heating feel weak.
To bleed: turn the heating off and let it cool. Hold a cloth under the bleed valve at the top of the radiator and turn the bleed key anticlockwise about a quarter-turn. Air will hiss out — when water starts to dribble, close it. Top up the system pressure to 1.2 bar afterwards.
If you find yourself bleeding the same radiators every few weeks, you have a sludge build-up that's drawing in air through micro-leaks — you'll need a power flush before the problem gets worse. This is incredibly common in Hertfordshire because of our very hard water (300–400ppm).
7. Look up the error code
Every modern boiler displays a fault code on the screen when something goes wrong. The codes vary by brand:
- F1 or F22: usually low water pressure (see check 1)
- F28: ignition failure — gas supply or flame sensor
- F75: pump or pressure sensor fault
- L2 (Worcester): no flame detected — gas valve or flame rod issue
- EA (Vaillant): flame loss — similar causes
A quick search of your boiler's model and the error code will usually tell you whether it's a check-yourself item or a genuine engineer job.
When to actually call us
After running through the above checks, call us if:
- The pressure won't hold (you have a leak somewhere)
- The boiler keeps locking out within minutes of resetting
- The fault code points to a sealed-system component (pump, fan, gas valve, heat exchanger)
- You smell gas — call us and the gas emergency line
- You have no hot water for more than a few hours and can't trace the cause
We offer same-day boiler repair across Hertfordshire — call 0208 092 1359 at any time. Standard rate is £95 + VAT for the first 30 minutes on site; out-of-hours emergency attendance (6pm–8am, weekends, bank holidays) is £145 + VAT. You can see the full rate card on our pricing page.
Prevention is cheaper than emergency repair
The single biggest preventer of mid-winter breakdowns is an annual boiler service. We charge £120 + VAT for a standard service or £170 + VAT bundled with a CP12 gas safety certificate (popular for landlords). It's a fraction of an emergency call-out, and it usually picks up the early warning signs of the problems that cause breakdowns — corroded electrodes, weak igniters, sticking gas valves, blocked condensate traps — months before they leave you cold.
Stay warm — and if any of the above describes your situation, give us a call.