No hot water and no heat
Taps stay cold, radiators are cold, and the boiler may be dark, quiet, or showing a fault.
Start here: Start with power, service switch, breaker, and the boiler display or fault light.
Boiler troubleshooting
Boiler No Hot Water
Direct answer: If your boiler has no hot water, the most common homeowner-level causes are the boiler being off or locked out, low system pressure, thermostat or timer settings, or a hot-water-only control problem. Start with the display, pressure gauge, and call-for-heat settings before you assume a major failure.
Most likely: On most residential boilers, the first useful split is simple: is the whole boiler not firing at all, or does space heat still work while domestic hot water does not? That tells you whether you are dealing with a basic power/lockout issue or a hot-water-side control problem.
A boiler that suddenly stops making hot water is often giving you a clue right on the front panel: low pressure, a lockout code, a reset light, or no sign of life at all. Reality check: many boiler hot-water complaints turn out to be a setting, pressure, or reset issue, not a failed boiler block. Common wrong move: pressing reset over and over without checking pressure, leaks, or whether the unit is trying to light and failing.
Don’t start with: Do not open combustion covers, work on gas valves, or start swapping boiler parts based on a guess. On boilers, that gets expensive fast and can get unsafe even faster.
If the boiler is completely deadCheck the service switch, breaker, and front-panel power before anything else.
If heat works but faucets stay coldFocus on the domestic hot water setting, timer, and call-for-hot-water side, not the whole heating loop.
Last reviewed: 2026-04-04
Figure out whether the boiler is fully down or just not making domestic hot water
Heat works but hot water does not
Rooms still heat normally, but showers and faucets never get hot.
Start here: Check whether the boiler is set to make domestic hot water and whether the problem is only on the hot-water side.
Hot water comes and goes
Water starts warm, then turns cool, or only gets hot for a minute.
Start here: Look for low pressure, lockout behavior, or a boiler that fires briefly and drops out.
Boiler shows pressure or fault warning
The front gauge is low, a reset light is on, or the display shows an error or lockout.
Start here: Read the pressure first, then decide whether a single reset is appropriate or whether the boiler needs service.
Most likely causes
1. Boiler power is off or the control is in lockout
When a boiler has no heat and no hot water, this is one of the first things to rule out. You may see a blank display, a reset light, or hear nothing at all when there should be a call.
Quick check: Confirm the service switch is on, the breaker is not tripped, and the boiler display is lit. If there is a lockout message, note it before touching reset.
2. Boiler system pressure is too low
Many boilers stop firing or make weak, inconsistent hot water when pressure drops too far. Low pressure often shows up after bleeding radiators or from a small leak.
Quick check: Look at the boiler pressure gauge when the system is cool. If it is well below the normal operating range marked on the gauge, low pressure is a strong suspect.
3. Timer, thermostat, or hot-water setting is wrong
A boiler can be healthy but not getting the right call for domestic hot water, especially after a power outage, seasonal setting change, or accidental control change.
Quick check: Make sure the boiler is not in summer or heating-only mode if it should be making domestic hot water, and verify any timer or programmer is actually calling for hot water.
4. Domestic hot water side is not responding even though the boiler still heats
If radiators heat but faucets stay cold, the fault is often on the hot-water demand side rather than the whole boiler. That can include a stuck diverter assembly, flow-sensing issue, or internal control fault.
Quick check: Run a hot tap and listen at the boiler. If nothing changes at the boiler while water is flowing, the hot-water call is likely not being recognized.
Step-by-step fix
Step 1: Confirm what is actually not working
You need to separate a whole-boiler shutdown from a hot-water-only complaint before you do anything else. The next checks are different depending on whether the radiators still heat.
- Turn on a hot faucet and let it run for a full minute to confirm the water truly stays cold or only gets lukewarm.
- If the home uses the boiler for space heat, check whether radiators or baseboards are heating at all.
- Look at the boiler front panel for lights, a display, a fault code, or a reset indicator.
- Listen for any response when there is a call for heat or hot water: fan noise, clicking, pump noise, or complete silence.
Next move: If you confirm the boiler is only failing on domestic hot water while space heat still works, stay focused on hot-water controls and settings. If neither heat nor hot water works, treat it like a whole-boiler shutdown and move to power, pressure, and lockout checks first.
What to conclude: This first split keeps you from chasing zone or radiator issues when the real problem is the boiler itself, or chasing boiler shutdown when only the hot-water side is affected.
Stop if:
- You smell gas anywhere near the boiler or meter area.
- You see water dripping onto wiring, controls, or the burner area.
- The boiler casing is hot, scorched, smoking, or making sharp banging noises.
Step 2: Check power, service switch, and obvious lockout
A boiler that is off, tripped, or locked out will not make hot water no matter what the thermostat says. This is the safest high-value check.
- Make sure the boiler service switch is on and has not been bumped off.
- Check the electrical panel for a tripped breaker. If it is tripped, reset it once only.
- Look at the boiler display or indicator lights and write down any fault code or message before pressing anything.
- If the manufacturer provides a normal user reset button and there is no gas smell or water leak, try one reset only.
Next move: If the boiler starts normally and hot water returns, monitor it closely. A one-time lockout can happen, but repeated lockouts mean the boiler needs service. If the breaker trips again, the display stays dark, or the boiler locks out again right away, stop there and call a qualified boiler technician.
What to conclude: A dead display points to power supply or internal electrical trouble. A repeat lockout points to an ignition, venting, sensor, or combustion-side problem that is not a safe DIY repair.
Stop if:
- The breaker trips a second time.
- The reset button does not restore operation and the boiler immediately faults again.
- You hear delayed ignition, booming, or repeated clicking without normal startup.
Step 3: Read the boiler pressure gauge before trying more resets
Low pressure is one of the most common reasons a boiler stops making reliable hot water, and it is easy to verify from the front of the unit.
- Find the pressure gauge or digital pressure reading on the boiler.
- Check the reading when the system is cool if possible.
- If the pressure is clearly below the normal marked range for the boiler, look around the boiler, nearby piping, and visible radiators or baseboards for signs of leakage.
- If your boiler has a clearly labeled homeowner filling loop and the manual allows user repressurizing, bring pressure back only to the normal range shown for the unit, then stop.
Next move: If pressure is restored and the boiler runs normally again, keep watching the gauge over the next day or two. Pressure that drops again usually means there is a leak or expansion-side problem that needs service. If pressure will not come up, rises too fast, or drops back down quickly, stop and schedule service instead of forcing more water into the system.
Stop if:
- You are not sure which valve is the filling loop.
- Pressure climbs rapidly toward the high end of the gauge.
- Water is leaking from the boiler, relief piping, or nearby fittings.
Step 4: Check the hot-water call settings and watch how the boiler reacts
When heat still works but hot water does not, the boiler may simply not be receiving or recognizing a domestic hot water demand.
- Verify the programmer, timer, or control is set to allow domestic hot water, not heating-only mode.
- If the boiler has separate heating and hot-water settings, make sure hot water is enabled and not turned all the way down.
- Run a hot faucet and stand near the boiler to see whether the display changes, a flame icon appears, or the unit starts a normal firing sequence.
- If nothing at all changes at the boiler while hot water is flowing but space heat still works, note that behavior for the service call.
Next move: If correcting the setting restores hot water, run several fixtures and make sure the boiler responds consistently each time. If the boiler still ignores a hot-water demand or fires only briefly and quits, the problem is likely inside the boiler's domestic hot water control path and is a pro repair.
Stop if:
- You would need to remove the boiler cover to continue.
- The boiler starts and stops rapidly, makes harsh noises, or shows a combustion-related fault.
- Any control wiring appears wet, burned, or loose inside the cabinet.
Step 5: Make the call: monitor a simple recovery or book boiler service
By this point you have ruled out the safe homeowner checks and narrowed the problem enough to avoid random parts buying.
- If the issue was a one-time setting change or a low-pressure correction and the boiler now makes steady hot water, keep using it while checking the gauge and watching for leaks.
- If the boiler has no power, repeated lockout, unstable pressure, or no response to a hot-water demand, book a qualified boiler technician and report exactly what you saw: pressure reading, fault code, and whether heat still works.
- If only one zone or one part of the house is cold while domestic hot water is fine, shift your troubleshooting to the distribution side instead of the boiler itself.
- If the system is noisy with air sounds or gurgling after pressure loss, address the air-in-system issue next rather than resetting the boiler repeatedly.
A good result: If hot water stays consistent through several cycles and the pressure remains stable, the immediate problem is likely resolved.
If not: If the problem returns, do not keep resetting or refilling the boiler. That usually points to a fault that needs proper testing.
What to conclude: Stable recovery after a simple correction is a good sign. Repeat faults, repeat pressure loss, or hot-water-only failure with normal heating usually mean an internal boiler component or control issue that is outside safe DIY work.
Stop if:
- Hot water returns only briefly and then fails again the same day.
- You need to add water repeatedly to keep the boiler running.
- The boiler shows new fault codes, leaks, or combustion symptoms at any point.
FAQ
Why does my boiler heat the house but not make hot water?
That usually points to a domestic-hot-water-side problem rather than a full boiler failure. Common examples are the hot-water setting being off, the boiler not recognizing a hot-water demand, or an internal diverter or sensing fault that needs service.
Can low pressure cause no hot water from a boiler?
Yes. Many boilers will not fire properly, or will make weak and inconsistent hot water, when system pressure drops too low. If pressure is low, correct it only if your boiler has a clearly labeled homeowner fill procedure and the manual allows it.
Should I press the reset button on my boiler?
One normal user reset is reasonable if there is no gas smell, no leak, and the manual allows it. If the boiler locks out again, stop there. Repeated resets do not fix the cause and can make the situation less safe.
What pressure should my boiler be at?
Use the range shown on your boiler gauge or in the manual. The exact target varies by system, so do not guess. What matters for troubleshooting is whether the reading is clearly below the normal marked range or will not stay stable.
When should I call a pro for a boiler with no hot water?
Call right away if you smell gas, see leaking around the boiler, get repeated lockouts, have a breaker that trips again, or have heat but no hot-water response after checking the settings. Those are not good guess-and-buy situations.
Could this be a plumbing problem instead of the boiler?
Sometimes. If the boiler appears to fire normally and other hot fixtures work, the issue may be local to one faucet or shower valve. But if no fixtures get hot and the boiler is not responding correctly, start with the boiler checks on this page.