I have a pretty old gas boiler at home and lately I've noticed it's running constantly, even if I close the doors to rooms I'm not using. My gas bill has gone up quite a bit. Is it normal for it to work like that or is there something I can check?
Don't try to adjust anything yourself if you have no idea how it works, but what you're describing sounds like the thermostat might be broken or out of adjustment, or maybe the three-way valve that controls the flow to the radiators isn't closing properly. Closing the doors to the rooms shouldn't keep the boiler running if it's already reached the temperature, so there's definitely something that needs checking. I'd recommend calling a technician because an old boiler running all day won't just spike your bill, it could also be a safety hazard ⚠️ In the meantime, try manually adjusting the temperature to see if it responds.
An old boiler running all day is almost always a broken or miscalibrated thermostat problem, but it could also be that the mixing valve is stuck and won't cut off the flow when it reaches temperature. What the previous comment says about not touching anything is right, but before calling a technician try something simple: manually turn the thermostat up and down a few degrees to see if the boiler responds, because if nothing changes that's confirmation it's damaged. If the boiler keeps doing the same thing anyway, then you really do need a professional because messing with valves without knowing what you're doing is dangerous.
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