Common Boiler Problems

Heating & Hot Water Problems

These are the most common boiler call-outs. Each has specific symptoms that point to different causes.

• No heat, boiler not firing: Check thermostat batteries and setting first. If thermostat is calling and boiler doesn't respond, possible causes: failed ignition, gas supply issue, frozen condensate pipe (common below 0°C), or locked-out boiler. Reset once — if it doesn't fire, call us.
• No hot water but heating works: On combi boilers, this usually means a failed diverter valve — the component that switches between heating and hot water. Also possible: blocked plate heat exchanger, failed flow sensor. Needs professional diagnosis.
• Hot water fluctuates hot-cold-hot: Classic symptom of a blocked plate heat exchanger — common in Vancouver homes where water quality causes scale buildup. Also possible: flow sensor issue or thermistor malfunction.
• Radiators cold at top, hot at bottom: Air trapped in the system. Bleed the radiator with a radiator key until water flows steadily. If problem recurs quickly, you have an air ingress issue — call us.
• Radiators cold at bottom, hot at top: Sludge buildup in the radiator. The hot water can't circulate through the sludge. Power flushing is the solution — not a DIY fix.
• One radiator cold, others hot: Check the thermostatic radiator valve (TRV) isn't stuck. Tap the valve body gently. If still cold with valve open, likely a blockage or balancing issue.
• All radiators cold, boiler running: Circulation pump failure, motorized valve stuck, or major airlock. The boiler is producing heat but it's not being distributed. Needs professional diagnosis.

Pressure Problems

Boiler pressure is the most common thing homeowners can check themselves. The pressure gauge should read 1.0-1.5 bar when cold.

• Pressure too low (below 0.8 bar): Top up via the filling loop (check your boiler manual for the filling loop location). If pressure drops again within days, you have a leak — call us to locate and repair it.
• Pressure too high (above 2.5 bar): Failed expansion vessel (lost air charge) or filling loop left open. Bleed a radiator to reduce pressure temporarily, but the root cause needs professional repair.
• Pressure rises when heating, drops when cold: Expansion vessel needs repressurizing or replacing. The vessel provides room for water to expand when heated. When it fails, pressure swings widely.
• Pressure gauge at zero: System has a significant leak or has been drained. Do not run the boiler at zero pressure — you can damage the pump and heat exchanger. Call us to diagnose and refill.

Noise Problems

Unusual boiler noises always indicate a mechanical issue. These are the most common sounds and their typical causes:

• Kettling / rumbling: Water can't flow fast enough through the heat exchanger — it's boiling locally. Cause: sludge buildup, failing pump, or blocked heat exchanger. Power flushing is the primary fix.
• Banging / knocking: Delayed ignition — gas builds up before igniting. Safety concern. Could be a dirty burner, incorrect gas pressure, or failing ignition electrode. Call us.
• Whistling / high-pitched squeal: Air in the system, partially closed valve, or failing pump bearing. Bleed radiators first; if noise persists, pump may need replacement.
• Gurgling: Air trapped in radiators or pipework. Bleed radiators. If water is murky or brown, system may need flushing.
• Vibrating / humming: Loose panels, failing pump, or pipework vibrating against walls. Check for loose casing screws first.

Error Code Problems

Modern boilers display error codes when they detect a fault. The code tells you what system triggered the lockout.

• Ignition failure (E003 on Navien, F4 on Viessmann): Boiler tried to light but failed. Could be gas supply, electrode, or control board. Reset once; if it returns, call us.
• Flame loss during operation (E012 on Navien): Flame went out mid-operation. Possible causes: gas pressure fluctuation, flame sensor dirty, or condensate blockage.
• Overheat lockout: Boiler exceeded safe temperature. Circulation problem — pump, blockage, or airlock. Do not repeatedly reset — you can damage the heat exchanger.
• Low water pressure (E302 on Navien, F22 on Viessmann): System pressure below minimum. Top up via filling loop. If it happens repeatedly, there's a leak.

Frequently Asked Questions