Step 1: Check the boiler pressure
Almost every domestic gas boiler has a pressure gauge or digital readout on the front panel. Healthy system pressure when the boiler is cold sits between 1.0 and 1.5 bar. Below 0.5 bar, most boilers refuse to fire to protect themselves. To top up: locate the filling loop (usually a small braided silver hose under the boiler with two valves on it), open both valves slowly until the pressure climbs to around 1.2 bar, then close both valves tight. Press the reset button on the boiler face. If the pressure climbs but the boiler still won't fire, move on to Step 2. If the pressure keeps dropping every few days, there's a leak somewhere — ring us.
Step 2: Check for a frozen condensate pipe (winter only)
Modern condensing boilers produce a small amount of liquid water (condensate) that drains via a small white plastic pipe — usually outside the property. When Aberdeen overnight temperatures drop below -2°C, the condensate inside that pipe freezes solid, the boiler can't discharge water and it locks itself out. You'll usually see a specific fault code: F22, F75 or LF depending on the brand. The fix is straightforward: locate the external condensate pipe, pour warm (not boiling) water along it for a few minutes until you hear the ice break, then reset the boiler. Lagging the pipe with proper insulation foam prevents it happening again.
Step 3: Reset the boiler
Most modern boilers have a reset button on the front panel — often a flame icon or the word 'Reset' on a separate button. If the boiler is showing any fault code, pressing reset clears it and lets the boiler attempt to ignite again. If it relights and runs fine, you had a transient fault and can carry on. If it goes back to the same fault code immediately, the underlying problem is real and needs a Gas Safe engineer. Don't keep pressing reset more than twice — repeated resets on a faulting boiler can lock the unit out permanently and a manufacturer-trained engineer needs to reset it.
Step 4: Check the thermostat and timer
Sometimes the boiler is fine but the thermostat is telling it not to fire. Common issues: room thermostat batteries dead, the dial is set lower than the room temperature, the timer is in 'off' mode, a holiday-mode setting wasn't cleared. Check the wall thermostat first — replace the batteries if it's a wireless one. Then check the timer. Some older mechanical timers stick when there's a power cut and need to be reset manually. Smart thermostats (Hive, Nest, Tado) occasionally lose connection — open the app and check the heating is set to 'on' and the schedule is active.
Step 5: Check the gas supply
If you have other gas appliances (a hob, a fire), test those. If the gas hob lights normally, gas is reaching the property and the issue is the boiler. If the hob also won't light, the issue is the gas supply — usually a closed isolation valve, a smart meter cut-off, or — rarely — a wider supply problem. The gas emergency line in Scotland is 0800 111 999 if you suspect a leak or smell gas. Don't try to investigate gas-supply issues yourself.
Common Aberdeen-specific factors
Aberdeen homes throw up a few region-specific causes for boiler trouble. Granite tenement properties with original 1950s-1970s heating systems often have undersized pipework that struggles when a modern condensing boiler is fitted — manifests as pressure cycling and lockouts. Coastal properties from Footdee to Cove Bay get accelerated flue corrosion from salt air, which can intermittently block the flue gas path. And the long Aberdeen winters mean condensate freeze is genuinely common from December through March — far more common here than in southern England.
When to call a Gas Safe engineer immediately
Some symptoms mean stop, switch the boiler off at the spur, and ring a Gas Safe registered engineer right away. Don't try to reset, don't ignore, don't wait until the morning:
- Smell of gas in or around the property — also ring 0800 111 999 (the National Gas Emergency line)
- Black soot marks on or around the boiler casing
- Yellow or orange flame inside the boiler (it should be blue)
- Boiler making a banging, popping or kettling noise
- Anyone in the house feeling drowsy, dizzy or experiencing headaches when the boiler runs
- Water leaking from the boiler unit (not the condensate)
What to tell us when you ring
If you've worked through the five steps and the boiler still won't fire, ring Belmont with three pieces of information ready: the boiler make and model (printed on a sticker on the front or underside), the fault code if any is showing, and what you've already tried. That lets us diagnose the likely fault on the phone and arrive with the right parts. Most calls we get fall into a handful of common patterns and we can usually quote the repair on the call.
Need this done in Aberdeen?
Ring Belmont. Gas Safe registered, no call-out charge, we answer the phone first ring.