Boiler completely dead
The display is blank, no lights are on, and nothing happens when the thermostat calls for heat.
Start here: Start with power at the service switch, emergency switch if present, and the breaker.
Boiler troubleshooting
Boiler Not Heating
Direct answer: If your boiler is not heating, start with the thermostat, power switch, breaker, boiler pressure gauge, and any obvious lockout or error light. Homeowners can safely handle those basic checks, but gas smell, water leaking from the boiler, repeated lockouts, or pressure problems that keep returning are service-call issues.
Most likely: The most common homeowner-level causes are thermostat settings, a tripped breaker or service switch, low boiler pressure, or a simple lockout that clears once and then stays running.
A boiler no-heat call can look like one problem when it is really several different ones. First figure out whether the boiler is completely dead, powered on but not firing, or making heat but not moving it through the house. That keeps you from chasing the wrong fix and helps you know when the safe next move is a reset, a pressure check, or a pro.
Don’t start with: Do not start by opening panels, bleeding components at the boiler, adjusting gas controls, or buying ignition, gas, or circulator parts based on a guess.
Boiler has no signs of life?Check the service switch and breaker before anything else.
Boiler powers on but house stays cold?Look at thermostat call, pressure, and any lockout light or code.
Last reviewed: 2026-03-31
What kind of no-heat boiler problem do you have?
Boiler has power but no heat call response
The display is on or lights are lit, but the boiler does not start heating when you raise the thermostat.
Start here: Check thermostat mode, setpoint, batteries if used, and whether another zone is calling.
Boiler fires or sounds active but rooms stay cold
You hear operation at the boiler, but baseboards or radiators stay cool or only partly warm.
Start here: Check system pressure and note whether the problem is whole-house or only one zone.
Boiler locks out or needs frequent resetting
A reset light, fault light, or code appears, or the boiler runs briefly and shuts down again.
Start here: Try one normal reset only if the label allows it, then stop if the fault returns.
Most likely causes
1. Thermostat setting or control issue
A boiler that has power but never starts on a heat call often is not receiving a proper call for heat.
Quick check: Set the thermostat to Heat and raise it several degrees above room temperature. Replace thermostat batteries if your model uses them.
2. Power loss to the boiler
A blank display or no lights often points to a tripped breaker, switched-off service disconnect, or emergency switch.
Quick check: Check the boiler service switch, nearby emergency switch, and the home's electrical panel for a tripped breaker.
3. Low boiler pressure or system water issue
Many boilers will not heat properly, or will lock out, when pressure drops too low.
Quick check: Look at the boiler pressure gauge when the system is cool. Very low pressure is a common no-heat cause.
4. Safety lockout or internal boiler fault
If the boiler tries to start, then stops, flashes a fault light, or needs repeated resets, a safety device or internal component may be shutting it down.
Quick check: Read the display or indicator lights, try one allowed reset, and see whether the boiler runs normally afterward or faults again.
Step-by-step fix
Step 1: Confirm the exact no-heat pattern
You need to separate a dead boiler from a control problem or a circulation problem before doing anything else.
- Set the thermostat to Heat and raise the setpoint at least 3 to 5 degrees above room temperature.
- Listen at the boiler for any response within a minute: click, fan, burner attempt, pump sound, or nothing at all.
- Check whether the problem affects the whole house or only one heating zone.
- Look for a display, status light, or fault light on the boiler without removing any covers.
Next move: If the boiler starts and heat begins moving, the issue may have been a thermostat setting or a temporary control hiccup. Keep watching it through a full heating cycle. If nothing changes, move to power and basic control checks next.
What to conclude: This tells you whether the boiler is dead, not getting a heat call, or failing after startup.
Stop if:
- You smell gas or exhaust fumes.
- You see smoke, scorching, or melted wiring.
- Water is leaking from the boiler jacket, relief piping, or nearby controls.
Step 2: Check power to the boiler
A switched-off service disconnect or tripped breaker is one of the fastest safe checks and can make the boiler look completely failed.
- Make sure the boiler service switch is on. It may look like a regular wall switch near the boiler.
- Check for an emergency switch at the top of basement stairs or near the mechanical area and make sure it is on.
- Check the electrical panel for a tripped breaker. Reset it once if it is tripped.
- If the boiler has a plug, make sure it is fully seated in the outlet.
Next move: If power comes back and the boiler runs normally, you likely had a simple power interruption. Watch for another trip or shutdown. If the breaker trips again, the display stays dead, or the boiler powers up but still does not heat, go to the next step.
What to conclude: Repeated breaker trips or dead controls point away from a simple thermostat issue.
Stop if:
- The breaker trips again after one reset.
- You hear buzzing, see arcing, or notice a burning smell.
- Any wiring looks wet or damaged.
Step 3: Check thermostat call and boiler pressure
These are the two most common homeowner-visible reasons a powered boiler still will not heat.
- Confirm the thermostat is in Heat mode and not on a schedule setback or vacation setting.
- Replace thermostat batteries if your thermostat uses them and the display is weak, blank, or acting erratically.
- Look at the boiler pressure gauge when the system is cool. Compare the reading to the normal operating range marked on the boiler label or gauge face if shown.
- If pressure is clearly very low, note it before doing anything else. Do not start opening valves unless you know your fill setup and the boiler manual allows homeowner repressurizing.
- If only one zone is cold while others heat, note that as a zone or circulation issue rather than a whole-boiler failure.
Next move: If correcting the thermostat setting restores heat, the boiler itself may be fine. If pressure was normal and all zones are still cold, continue to lockout checks. If pressure is low, or one zone stays cold while others work, stop short of invasive work and arrange service unless you are already familiar with your exact fill procedure.
Stop if:
- The pressure gauge is near zero or dropping steadily.
- The pressure is unusually high or relief piping is dripping.
- You are not certain which valve is the system fill valve.
Step 4: Check for a simple lockout and try one reset only
Some boilers shut down after a failed ignition attempt or another safety event. One normal reset can tell you whether it was temporary or not.
- Look for a reset button, fault light, or display message on the user-accessible control area.
- If the boiler label or user instructions allow it, perform one normal reset only.
- After resetting, stay nearby and listen for what happens next: normal startup, repeated clicking, brief firing then shutdown, or no response.
- Do not press reset repeatedly if the boiler does not stay running.
Next move: If the boiler starts and completes a normal heating cycle, the lockout may have been temporary. Keep an eye on it over the next day. If it locks out again, clicks without lighting, starts then shuts down, or shows the same fault, stop DIY and book service.
Step 5: Decide between safe handoff paths
At this point you have ruled out the simple homeowner checks and need the right next move instead of guessing at parts.
- If the boiler is dead after power checks, use the broader no-operation path for full-system troubleshooting.
- If the boiler has low pressure, recurring lockouts, leaks, or only one zone is not heating, schedule boiler service and tell them exactly what you observed.
- If the boiler briefly worked after a reset but failed again, report the fault light or code and the startup behavior you heard.
- Until service arrives, keep the thermostat at a steady setting and do not keep resetting the boiler.
A good result: If a technician-level issue is confirmed, you avoided unnecessary parts and gave a cleaner service call description.
If not: If you still cannot tell whether the boiler has power at all, move to the broader no-operation guide next.
What to conclude: The safe next move is now a targeted handoff, not more trial-and-error.
Stop if:
- You are considering opening combustion panels or adjusting gas controls.
- You plan to keep resetting the boiler to force heat.
- The leak, pressure problem, or fault condition is getting worse.
FAQ
Why is my boiler on but not heating the house?
If the boiler has power but the house stays cold, the usual homeowner-visible causes are no thermostat call, low system pressure, a lockout condition, or a single-zone circulation problem. Start by checking thermostat settings, the pressure gauge, and any fault light or reset indicator.
Can low pressure make a boiler stop heating?
Yes. Many boilers will not run properly, or will lock out, when system pressure drops too low. If the gauge is clearly low, do not guess at valves unless you already know your exact fill procedure. A pressure loss that returns usually means the system needs service.
Should I keep pressing the boiler reset button?
No. One normal reset is reasonable if the boiler label or manual allows it. If the boiler locks out again, stop there. Repeated resets can hide the real problem and may be unsafe on a combustion appliance.
What if only one zone is not heating?
That usually points away from a whole-boiler failure. A single cold zone can mean a thermostat issue for that zone, a zone valve problem, air in that loop, or a circulator-related issue. That is usually a service diagnosis rather than a parts-guess situation.
When should I call a pro for a boiler not heating?
Call for service right away if you smell gas or fumes, see water leaking from the boiler, have repeated lockouts, have very low or very high pressure, or the breaker keeps tripping. Also call if the boiler has power but still will not heat after the basic thermostat, power, and one-time reset checks.