Boiler not heating radiators are cold — radiators are cold

Use only checks that match the exact appliance or system and its official guide.

1. Check 1

   Set the room thermostat above the current room temperature and check the programmer or timer for an active central-heating period. Confirm that the boiler is not set to hot-water-only, holiday, summer, or another mode that excludes radiator heating, using only the normal user controls and the appliance manual.

   Expected result: The heating demand was off or scheduled later, the boiler was in a non-heating mode, or the controls are calling for heat but the boiler and radiators remain cold.

   Next step: Correct only the user-accessible setting described by the manual and observe one normal heating cycle. If the boiler does not respond or the setting will not hold, record it and arrange qualified service.

   Stop if: Stop if controls are damaged, wiring is exposed, the boiler behaves abnormally, or changing the setting would require opening a cover or altering internal wiring.

   Why this matters

   Why: A disabled demand or wrong mode can explain cold radiators without a boiler breakdown; a valid demand with no response shifts concern toward boiler status, power, pressure, or circulation.

2. Check 2

   Read the boiler display and indicator lights without removing the casing. Record any fault code, lockout symbol, pressure warning, unusual noise, repeated start attempts, or whether hot water still works while central heating does not. Check the manual for the meaning of the exact code rather than guessing from a generic list.

   Expected result: The boiler shows a returning fault or lockout, no demand response, a pressure warning, or normal status despite cold radiators.

   Next step: Record the exact display and arrange qualified heating service for a fault, lockout, or no response. Do not keep resetting the boiler or attempt to repair the ignition, burner, pump, sensor, or control board.

   Stop if: Stop immediately for gas smell, smoke, burning odor, unusual flame, carbon-monoxide alarm, water escaping from the boiler, or an electrical smell or hazard.

   Why this matters

   Why: A returning fault or lockout is a boiler-service clue; normal status with cold radiators makes control, valve, pressure, or circulation checks more relevant but does not make internal repair safe.

3. Check 3

   Read the pressure gauge or digital pressure display and look from a safe position for visible leaks at accessible radiator valves, pipe joints, and beneath the boiler. Compare the reading with the normal range in the exact appliance manual; do not remove the casing or operate an unfamiliar filling control.

   Expected result: Pressure is below or above the manual's normal range, has dropped since a previous check, or appears normal with no visible leak.

   Next step: Photograph the display and any visible water, keep the heating off if water is escaping, and contact a qualified engineer. Only follow a documented manual procedure for a one-time user-level pressure correction when the system is cool and no leak is suspected; otherwise ask the engineer to do it.

   Stop if: Stop for active leakage, rapid pressure change, hot discharge, damaged pipework, electrical contact with water, or any need to open the boiler or manipulate an unknown valve.

   Why this matters

   Why: An abnormal or changing reading can indicate lost system water, a leak, or another system fault; normal pressure does not rule out a failed boiler, valve, pump, or circulation problem.

4. Check 4

   With the heating off and radiators cool, check the accessible manual or thermostatic valve on each affected radiator for a closed or very low setting, a stuck control, or furniture blocking the radiator. Compare one affected radiator with a normally warm one without removing the valve or pipework.

   Expected result: Only one radiator is cold, several radiators on one area are cold, a valve is closed or restricted, or all radiators are equally cold despite open controls.

   Next step: Restore only an obviously closed user control and observe a normal cycle. If the valve is stuck, leaking, or the radiator stays cold, ask a heating engineer to inspect the valve and circulation; do not remove or force it.

   Stop if: Stop for a leaking valve, hot surfaces, damaged pipework, a valve that will not move normally, or any need to drain the system or remove a component.

   Why this matters

   Why: A local valve or flow issue is more likely when the boiler and other radiators work; many equally cold radiators point back toward shared heating demand, boiler, pressure, or circulation rather than one radiator valve.

5. Check 5

   If one radiator is partly warm and the system manual permits user bleeding, first turn the heating off and let the radiator cool, then follow the exact manufacturer procedure while protecting the surrounding surface. Compare the temperature pattern: top colder than bottom, bottom colder than top, or cold throughout. Do not bleed a hot radiator or continue if the valve leaks.

   Expected result: Air escapes and the radiator later warms more evenly, the radiator is cold at the bottom but warm at the top, or bleeding changes nothing and multiple radiators remain cold.

   Next step: After any permitted bleeding, check pressure as the manual directs and stop if it falls or the radiator remains abnormal. Arrange qualified service for sludge, repeated air, leaks, or multiple cold radiators.

   Stop if: Stop for hot water, a seized or leaking bleed valve, damaged threads, abnormal pressure, repeated need to bleed, or any attempt to add chemicals or flush the system without professional guidance.

   Why this matters

   Why: A top-cold/bottom-warm pattern is consistent with trapped air; bottom-cold/top-warm can indicate sludge or poor circulation; no improvement or whole-system coldness points toward a broader fault needing diagnosis.