Why is my boiler not heating the house?
There are few worse feelings than a cold house on a chilly Metro Vancouver morning, especially when the boiler seems to be running but no warmth reaches the rooms. The good news is that a boiler failing to heat the house usually comes down to a manageable list of causes, and several of them you can check yourself in a few minutes.
The key is to work through them systematically, from the simplest settings to the mechanical parts, so you know whether it is a quick fix or a job for a professional. This guide walks Metro Vancouver and Fraser Valley homeowners through the common reasons a boiler is not heating the house, what to check safely, and when to call a licensed, insured technician. HeatLand has restored heat to local homes on all major boiler brands since 1999.
Start with the simple settings and pressure
Before assuming the worst, rule out the easy causes. Check the thermostat is set above the current room temperature and switched to heat mode, and that it has working batteries if it is battery-powered. Confirm the programmer or timer is actually calling for heat at this time of day and has not slipped its schedule, common after a power cut. Make sure the boiler has power and gas and is not showing a fault code. Then look at the pressure gauge; if it reads below about 1 bar, low pressure may be stopping the boiler from firing, and topping up via the filling loop to 1.2 to 1.5 bar may restore heat. Also check whether any fault or lockout code is displayed, and try a single reset per the manufacturer’s instructions. A surprising number of no-heat calls come down to a setting, low pressure, or a resettable lockout, so these quick checks are always worth doing first.
Cold radiators, air, and sludge
If the boiler is firing but rooms stay cold, the problem may be in the radiators or circulation. Radiators that are cold at the top but warm at the bottom usually have trapped air, which you can release with a radiator bleed key; be ready to top the pressure back up afterward. Radiators that are cold at the bottom but warm at the top often have sludge buildup restricting flow, which needs a power flush by a technician. If some rooms heat while others stay cold, the system may need balancing so hot water is distributed evenly. If no radiators warm up at all despite the boiler running, circulation itself has likely failed, pointing to the pump or a valve rather than the radiators. Bleeding and checking radiators is safe DIY, but a full power flush, balancing, or pump work should be left to a professional. Note whether the problem is one room, several rooms, or the whole house, as that narrows the cause considerably.
Pump, valves, and boiler faults
When the boiler runs but no heat circulates anywhere, the usual culprits are the circulating pump, a diverter valve, or a zone valve. The pump moves hot water around the system; if it has seized or failed, water heats in the boiler but never reaches the radiators. A diverter valve directs flow between heating and hot water, and if it sticks toward hot water, the radiators get nothing, sometimes you have hot taps but a cold house. Motorized zone valves that fail closed will leave whole zones unheated. These components involve electrical and, on gas boilers, gas-safety considerations, so diagnosis and replacement should be done by a licensed technician. In British Columbia, gas boiler work must be performed by a licensed gas fitter, and HeatLand’s technicians are TSBC-certified. Safety note: if you smell gas, notice scorching, or have symptoms of carbon monoxide such as headaches or dizziness that ease when you leave the house, shut the boiler off, leave, and call your gas utility and a technician immediately.
Quick Checklist
- Set the thermostat above room temperature, in heat mode
- Confirm the programmer is calling for heat now
- Check pressure and top up to 1.2 to 1.5 bar if low
- Bleed radiators that are cold at the top
- Note if it is one room, several rooms, or the whole house
- Call a technician if the boiler runs but no radiators warm up
| Symptom | Likely cause | Action |
|---|---|---|
| Boiler will not fire | Thermostat, low pressure, lockout | Check settings and pressure (DIY) |
| Radiator cold at top | Trapped air | Bleed radiator (DIY) |
| Radiator cold at bottom | Sludge buildup | Power flush (pro) |
| No radiators warm, boiler runs | Pump or valve failure | Diagnose and repair (pro) |
| Hot water fine, house cold | Stuck diverter or zone valve | Repair (pro) |
Frequently Asked Questions
Why is my boiler on but the house is cold?
If the boiler fires but rooms stay cold, hot water is being made but not circulated to the radiators. Common causes are a failed circulating pump, a stuck diverter or zone valve, or air and sludge blocking flow. Bleed radiators and check pressure first; if no radiators warm up at all, a licensed technician should check the pump and valves.
Why is only one room not heating?
A single cold room usually means a local radiator problem, trapped air at the top, sludge at the bottom, a closed or stuck valve, or the system needing balancing so that room gets its share of hot water. Bleeding the radiator and opening its valves fully often helps. If it stays cold, the radiator may need flushing or balancing by a technician.
Can low pressure stop my boiler from heating the house?
Yes. Many boilers will not fire when pressure falls below about 1 bar, so the house stays cold. Check the gauge and, if it is low, top up via the filling loop to 1.2 to 1.5 bar and reset the boiler if needed. If pressure keeps dropping and heat keeps failing, there is likely a leak that a technician should find and fix.
Should I call someone if the boiler runs but there is no heat?
If you have checked the thermostat, programmer, pressure, and bled the radiators but the house still will not warm, yes, call a licensed technician. A boiler that runs without circulating heat usually has a pump or valve fault that needs professional diagnosis. HeatLand serves Metro Vancouver and the Fraser Valley and offers emergency service when you are left without heat.
Reviewed by the HeatLand Heating & Cooling team — licensed HVAC contractor serving Metro Vancouver & the Fraser Valley since 1999. This article is for general guidance only. If you smell gas, suspect a carbon monoxide leak, or are unsure about any electrical or gas component, stop troubleshooting immediately and call a licensed technician or 911.