What should I do if my boiler is not heating?

What this symptom usually means on a boiler system

When a boiler is not heating, the problem is usually somewhere in the heat-making or heat-moving path: the thermostat or zone control may not be asking for heat, the boiler may not be firing, or the hot water may not be circulating through the home. That is different from a leak, a pressure-only complaint, or a noise-only complaint because the defining symptom here is simple: the living space stays cold even though the system should be producing heat.

What to look for before the service visit

If the whole house is cold, watch what happens after you raise the thermostat 3 to 5 degrees. A healthy system should usually show some response within a few minutes: a zone valve moves, a circulator starts, or the boiler begins a firing sequence. If nothing changes at all, the issue is often the thermostat circuit, transformer, relay, or zone control. If the boiler starts but radiators or baseboards stay cool, circulation or water-pressure problems move higher on the list.

If only one room or one zone is cold, the problem is less likely to be the main boiler and more likely to be a stuck zone valve, air in that loop, a failed circulator assigned to that zone, or a closed balancing valve left from prior service. In homes with baseboard or radiators, one cold section next to several warm ones usually points to flow trouble rather than a burner problem.

Boiler pressure matters because hydronic heat depends on water volume and movement. Many residential systems run around 12 to 20 psi when cool to moderately warm. If the gauge is notably below normal, the boiler may lock out, short-cycle, or fail to push heat to upper floors. If the pressure looks normal but the boiler cabinet is warm and supply piping is hot while rooms remain cold, a circulator or zone-flow issue becomes more likely.

How technicians usually diagnose a no-heat boiler call

A technician will typically verify the call for heat from the thermostat and zone controls, check boiler pressure and temperature, confirm whether the circulator is running, and test the ignition and safety sequence. On zoned systems, they may check whether each valve opens fully and whether hot water is actually moving through the branch that serves the cold area. If air is suspected, they may purge the loop and confirm the feed and expansion components are working correctly.

What usually affects repair cost

Cost depends on which part of the heating chain has failed. A thermostat, relay, or zone valve head is often less costly than replacing a circulator pump, control board, or ignition assembly. Typical 2025-2026 U.S. repair ranges are roughly $150-$400 for thermostat or control-call issues, $250-$700 for zone valve or air-purge work, $500-$1,200 for many circulator pump replacements, and $300-$1,500+ for ignition or boiler control repairs, with higher totals possible on older or high-end systems. Access to piping, number of zones, boiler type, and whether parts are OEM-specific also change the price.