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Boiler fires up intermittently

Hello
We have a slant fin gas boiler, around 18 years old. Connected to a nest thermostat.

The past week or so when we wake up in the morning the thermostat will show its heating but the house temp is a few degrees below the set temp.

The boiler is not heating but the damper light seems to be on and it sounds like a fan is running. It will do this for hours. If we turn off and on the boiler you can hear what sounds like the damper opening/closing and then within a few minutes the boiler ignites and begins heating up to the set point.

During the day sometimes it will fire up when called for heat and sometimes it repeats the process above.

It's almost as if the damper switch or sensor is faulty so it won't start ignition.

Any thoughts ?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 22,181
    I presume this is a boiler with a motorized exhaust damper? Those dampers have an end switch, which is supposed to close when they are fully open. Those end switches are somewhat less than reliable. Is there a manual way you can lock it open? Perhaps a switch on it to force it to open manually? Then the boiler should operate normally.

    Or replace the end switch -- or the whole dang damper. I never liked those things. More trouble than they're worth.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    unclejohnSuperTechnorthernsoul
  • northernsoul
    northernsoul Member Posts: 134
    The damper pipe does have a box on it and I think you can turn a dial to open/close etc. Would the green light mean it's open? I'll have to take a closer look at it tonight . I'm new to boilers in this new house
  • Jamie Hall
    Jamie Hall Member Posts: 22,181
    Probably... a picture would be helpful, if you can.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 14,560
    It sounds like ignition is failing. when you shut the switch off and back on the boiler starts because you are resetting the control

    You need a qualified technician to service this thing
    northernsoul
  • northernsoul
    northernsoul Member Posts: 134
    Had the boiler looked at and it was a faulty mercury flame sensor - pilot would light but never ignite burners. Had replaced.

    The other suggestion he had was a new auto feed valve. The pressure in my boiler running hot is normally only around 12. Some of the upstairs cast iron rads only heat halfway. Looks like the feed valve is faulty and isn't keeping the pressure up enough.

    I think it should be up around 15 based on our house height
  • ratio
    ratio Member Posts: 3,553
    If the pressure is going down but the system is still hot, water is leaking out. New water is the bane of boilers, it can cause failures in just a few years. Check the low water cutoff for correct operation (important!), then close the valve on the feeder & keep an eye on the pressure as the system operates. It shouldn't drop a significant amount over the course of the season, let alone a few days.
    northernsoul
  • northernsoul
    northernsoul Member Posts: 134
    > @ratio said:
    > If the pressure is going down but the system is still hot, water is leaking out. New water is the bane of boilers, it can cause failures in just a few years. Check the low water cutoff for correct operation (important!), then close the valve on the feeder & keep an eye on the pressure as the system operates. It shouldn't drop a significant amount over the course of the season, let alone a few days.

    Thanks - where would water be leaking out from? I don't see any leaks in piping near the boiler and nothjng from any of the rads- maybe a pipe in the wall?
  • ratio
    ratio Member Posts: 3,553
    Does the pressure in fact drop during operation? Set too low is a different issue than leaking out. 12# will put the water level over 25' above the water feeder, which (the water level) must be ±5' above the highest radiator.

    WRT the pressure, there will be some variation from warm to cold (& it may take some hours to drop from warm to cold), but it should go back to a similar pressure once it heats again. The water doesn't get used up, if you find yourself adding all the time, it's leaking out somewhere.

    As for where, that's a harder question. A close visual inspection is called for, for concealed pipes a moisture tester or a thermal camera is helpful.

    How 'bout some pics of the boiler, showing the piping?

  • northernsoul
    northernsoul Member Posts: 134
    > @ratio said:
    > Does the pressure in fact drop during operation? Set too low is a different issue than leaking out. 12# will put the water level over 25' above the water feeder, which (the water level) must be ±5' above the highest radiator.WRT the pressure, there will be some variation from warm to cold (& it may take some hours to drop from warm to cold), but it should go back to a similar pressure once it heats again. The water doesn't get used up, if you find yourself adding all the time, it's leaking out somewhere.
    >
    > As for where, that's a harder question. A close visual inspection is called for, for concealed pipes a moisture tester or a thermal camera is helpful.
    >
    > How 'bout some pics of the boiler, showing the piping?

    Sure - you need a pic of all sides?

    Boiler was just running now up at 15 PSI, whereas this morning it was about 12. Hmmmm
  • ratio
    ratio Member Posts: 3,553
    Mostly the piping, but an overall shot from further back on the sides is helpful too.

    A 2# increase doesn't sound too bad to me. What was the water temp at 12# & again at 15#? Was the boiler firing, pump running?

  • northernsoul
    northernsoul Member Posts: 134
    > @ratio said:
    > Mostly the piping, but an overall shot from further back on the sides is helpful too.A 2# increase doesn't sound too bad to me. What was the water temp at 12# & again at 15#? Was the boiler firing, pump running?

    Okay will do -
    At 15# it was about 143
    At 12# not 100% sure but I'm guessing around 130-135

    in dead of winter when it was -5 out , the highest I ever noticed was around 150 degrees
  • ratio
    ratio Member Posts: 3,553
    I don't think I'd be worried about the pressure, other than a) check that it's sufficient, i.e. the elevation between the pressure reducing valve (probably the auto feeder) and the highest bleeder on the system is less than about 22 feet, and b) if I had to keep adding water to the system.

    The temperatures seem low however for a cast iron non-condensing boiler. Is this on an ODR, where the supply temp is lower during colder times and higher during warmer times?

  • northernsoul
    northernsoul Member Posts: 134
    > @ratio said:
    > I don't think I'd be worried about the pressure, other than a) check that it's sufficient, i.e. the elevation between the pressure reducing valve (probably the auto feeder) and the highest bleeder on the system is less than about 22 feet, and b) if I had to keep adding water to the system.The temperatures seem low however for a cast iron non-condensing boiler. Is this on an ODR, where the supply temp is lower during colder times and higher during warmer times?

    I don't think it has an ODR / but how can I check that? Is there a gauge outside ?
  • ratio
    ratio Member Posts: 3,553
    The controls, probably a medium/small box, would have a wire going to an outdoor sensor.
  • northernsoul
    northernsoul Member Posts: 134
    > @ratio said:
    > The controls, probably a medium/small box, would have a wire going to an outdoor sensor.

    The only boxes I see are the water level control box and the damper control. The boiler is 18 years old so I'm guessing no ODR
  • ratio
    ratio Member Posts: 3,553
    That's what I guess too, which is why I wonder why the temp is so low. Note, it may very well be just fine, it just sounds uncommonly low for what I'm expecting to see.
  • northernsoul
    northernsoul Member Posts: 134
    > @ratio said:
    > That's what I guess too, which is why I wonder why the temp is so low. Note, it may very well be just fine, it just sounds uncommonly low for what I'm expecting to see.

    Maybe the burners and combustion area need To be cleaned? Can a tech turn up the flame ?
    Thanks ! I'm new to boiler heating - always had either electric, or forced air
  • ratio
    ratio Member Posts: 3,553
    I would've expected your tech to mention cleaning if it were indicated when he was there.

    It's not a matter of turning up the flame, but setting the water temp higher, probably by an aquastat. IF that's really an issue. Remember, I'm just wondering about the low-sounding temp. It could just as easily be an out of calibration thermostat, or maybe I'm off base entirely. Hard to tell from 4000 miles away.

    northernsoul
  • SuperTech
    SuperTech Member Posts: 2,032
    Sounds like an aquastat issue.
    northernsoul
  • northernsoul
    northernsoul Member Posts: 134
    > @ratio said:
    > I would've expected your tech to mention cleaning if it were indicated when he was there.It's not a matter of turning up the flame, but setting the water temp higher, probably by an aquastat. IF that's really an issue. Remember, I'm just wondering about the low-sounding temp. It could just as easily be an out of calibration thermostat, or maybe I'm off base entirely. Hard to tell from 4000 miles away.

    The tech did recommend a cleaning - so we will be having them scheduled to do that shortly.
    Will upload some pics tomorrow when the light is better in the boiler room. Thanks!
    SuperTech
  • northernsoul
    northernsoul Member Posts: 134
    > @ratio said:
    > I would've expected your tech to mention cleaning if it were indicated when he was there.It's not a matter of turning up the flame, but setting the water temp higher, probably by an aquastat. IF that's really an issue. Remember, I'm just wondering about the low-sounding temp. It could just as easily be an out of calibration thermostat, or maybe I'm off base entirely. Hard to tell from 4000 miles away.

    Attaching some pics in this thread if it helps as well ratio
    Thanks!!
  • ratio
    ratio Member Posts: 3,553
    I don't see an aquastat in those pics. It'd be a strapped on to the pipe that leaves the top of the boiler, or mounted on a well (= port into the side of the pipe).

    WRT the fill pressure, do you get water out of the bleeders on the upper radiators, or nothing?

  • northernsoul
    northernsoul Member Posts: 134
    We were able to bleed all but one in the fall , which is the one that rarely heats all the way across. It did fully heat up when the pressure was up around 18 once
  • ratio
    ratio Member Posts: 3,553
    When you say "across", you mean side to side, or over and under? If the top half was cold and the bottom half hot, that would indicate you need more static fill pressure. If side to side, it might be due to low flow; with the pressure rising higher that sounds like a long run time which would allow a low flowing radiator to heat more.

    Does the room stay comfortable? are any parts too hot or too cold? Do you use a setback at night/during the day?

  • northernsoul
    northernsoul Member Posts: 134
    > @ratio said:
    > When you say "across", you mean side to side, or over and under? If the top half was cold and the bottom half hot, that would indicate you need more static fill pressure. If side to side, it might be due to low flow; with the pressure rising higher that sounds like a long run time which would allow a low flowing radiator to heat more.Does the room stay comfortable? are any parts too hot or too cold? Do you use a setback at night/during the day?

    Side to side - the one rad (which is about 6 feet long with 4 ribs) only goes about 1/3 to 1/2 warm.
    That room is always cooler which is ok for sleeping but not that comfortable during cold days.

    We keep the temp 5-6 cooler during the day . It usually takes a good 90 min at least minutes to raise the temp back up
  • ratio
    ratio Member Posts: 3,553
    Hydronic systems don't respond well to deep setbacks. 1-2° shouldn't be a problem unless your boiler is sized pretty closely to the heat loss of the house (most are anywhere from oversized to massively oversized), but 5-6° is a lot. That said, I don't see any reason to change it now other than you might be a little more comfortable if you reduce it somewhat. Do it one degree every week or so and your SO might not even notice!

    Does the burner on the boiler run the entire time it's recovering, the full 90 minutes, or does it cycle on & off during that time?

  • northernsoul
    northernsoul Member Posts: 134
    So Better to only have the temp set back a few degrees when we are away?
    The boiler will have the burner on the whole 90 min until the set thermostat temp is reached.
    After it goes it takes a while before the rads start feeling warm

    Our rad output is 80000btu and we have a small 2 story double brick home (no wall insulation) around 1500 ft b
  • ratio
    ratio Member Posts: 3,553
    If you're only gone during the day, I don't think there's a lot of fuel savings, and as you noticed there are comfort issues.

    Hydronic systems are slow to respond, they put out a slow steady heat once they're up to temp, and stay hot after the boiler shuts off. The closer the boiler is sized to the heatloss of the house the slower the system can respond.

    northernsoul
  • the_donut
    the_donut Member Posts: 374
    Not a fan of setbacks on any system. If air was all that was heated, setbacks would be fine, but most steam systems are in masonry faced or constructed buildings (in my neck of the woods). There's a lot of thermal mass to cool and heat, much more so than the air.

    True comfort comes from the radiative equilibrium, which 50% of body heat loss. Thata wht radiant heat feels so good at a lower air temp. During setback walls cool off then the air. The walls and ceiling cool off a larger amount than then air and require longer to reheat. You have to overcome lost thermal energy in walls to get back level of comfort during system down time. The only time setback makes sense to me is during a vacation where radiative losses will be reduced proportional to difference in outside temperature and house. You can cut your heat loss significantly by lowering the delta temperature.
    northernsoul
  • northernsoul
    northernsoul Member Posts: 134
    Thanks - I need to have the tech come back. It seems to take far too long to get the return temp up to 140-150
    Maybe a good cleaning will help

    Is there a downside to me opening up the aquastat inside the boiler and seeing what the hi low settings are. ?
  • northernsoul
    northernsoul Member Posts: 134
    > @the_donut said:
    > Not a fan of setbacks on any system. If air was all that was heated, setbacks would be fine, but most steam systems are in masonry faced or constructed buildings (in my neck of the woods). There's a lot of thermal mass to cool and heat, much more so than the air.
    >
    > True comfort comes from the radiative equilibrium, which 50% of body heat loss. Thata wht radiant heat feels so good at a lower air temp. During setback walls cool off then the air. The walls and ceiling cool off a larger amount than then air and require longer to reheat. You have to overcome lost thermal energy in walls to get back level of comfort during system down time. The only time setback makes sense to me is during a vacation where radiative losses will be reduced proportional to difference in outside temperature and house. You can cut your heat loss significantly by lowering the delta temperature.

    Great points thanks - we are in a double brick only old house that is in a cold winter climate. The walls are always cold in winter