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Oil-fired boiler coming on every few minutes despite settings at 3 cycles per hour

Hi there -

First time homeowner, no experience with boilers / furnaces. I feel that my boiler comes on too frequently and may be burning too much oil. I also would like advice on how best to control my zones for the most efficient heating of the house.

Here's my set-up (long, but I hope thorough!):

- The house is a 2450 sq ft bungalow. The fully finished / mostly insulated concrete basement level is in the ground in front, walk-out in back (sloped property). This level is about 1200 sq ft and the main floor about 1250 sq ft.

- I'm in southern Nova Scotia, Canada. Winters are cold but much milder than the interior of the continent, and very rainy / often snowy. The coldest months are January and February with average temperature of 1C / 34F. Temps can swing wildly from 10C / 50F one day to -10C / 14F the next, but temps below about -10C are quite rare, and never happen outside of Jan / Feb.

- The house is 60+ years old but is warm / well insulated enough that the boiler can be turned off May through October, inclusive, and generally only needs to be heated November through April. It also stays pleasantly cool inside during the not terribly hot but quite humid summers.

- I have hot-water baseboard heating powered by a Slant/Fin oil-fired boiler model XL-30-XP with a Riello 40 F5 burner with an "effective output" of 105,000 to 210,000 BTU/hr with 86% efficiency. This seems rather oversized to me based on some online calculators I've tried, but they all say something different, so I guess I need an expert opinion. The household hot water heater is separate, electrical.

- The boiler feeds 3 heating zones, 1 downstairs and 2 upstairs, each with Honeywell RTH2310 programmable thermostats I installed last year. (They aren't the best, I now realize, but they will stay for now.) The thermostats are all set for 21C / 70F during weekends and weekday mornings / evenings, and at just 16C / 61F other times. All set for 3 heating cycles per hour (used to be 4 until I realized that hot water systems can be set to 3).

So, my questions:

1. Having said all of that, during the months that it is turned on, the boiler seems to come on every few minutes and stay on for just a couple of minutes each time. The house heats up fairly quickly given the large temperature difference I have programmed. There are no noticeable temperature fluctuations in the house, so I'm thinking that the thermostats aren't registering drops in temperature often enough to account for all the times it comes on.

(Even during the months of May through August, when all of the thermostats were turned OFF, the boiler came on frequently enough to burn 320 litres / 84.5 gallons of oil. This seemed really excessive. I have since learned that my cast iron boiler can be safely switched off during warm months, so I won't have that problem again.)

Is the boiler too powerful for my needs, and short-cycling? Could it be each of the three zones calling for heat at different times? If so, is this even a bad thing? I'm not sure how much extra fuel might be getting burned, if any, or if the frequent burning is actually a good sign of efficiency? Should there be some way of synching the three zones so that they are on the same cycle (but then what's the point of having separate zones?)

2. I'm also curious if anyone has thoughts about the best heating plan for my house. I've been experimenting to see what seems to work best:

- Last year, my first year in the house, I tried keeping one upstairs zone of the house (which contained my office where I spent most of my time) at 21C / 70F, and allowed the rest of the house stay around 17C / 63F. I burned about 1885 litres / 498 gallons of fuel oil during the period October through May.

- This year I decided to heat the entire house to 21C / 70F. I have so far burned about 1126 litres / 297 gallons of oil during November through early February. As March and April are not nearly as cold as Jan / Feb, I'd predict my total by the end of the year will still be less than 2000 litres / 528 gallons - not much different from last year when I was so tight with the heat!

- My idea is that next winter I will try heating the downstairs zone to 21C / 70F and set the upstairs zones lower, and see how that works out. Heat rises...

Any opinions on whether any of this is worthwhile? Is it probably most efficient to just heat the whole house and not worry about it?

Many thanks,



  • chapchap70
    chapchap70 Member Posts: 139
    Quick thoughts

    580 gallons ain't bad for Nova Scotia for a 2450 sq foot home.

    84 gallons for May through August seems about right for a regular cast iron boiler especially if you are using it for hot water.

    It may or may not be warmer this winter than last winter so the comparisons from setting the thermostats differently might not be accurate.
  • warm winter...

    thanks chapchap. glad to hear my usage doesn't seem excessive. i've heard similar from other people.

    this winter has been very mild, so you're right - hard to compare to last year. I'd say I'm burning a bit more oil despite warmer weather, so heating the whole house might not be the best.

    my biggest neurosis is still hanging on just how often the boiler fires. sometimes it seems constant and i can hear my money burning away...
  • hot water separate

    the hot water system is separate from the boiler. electrical. not sure why. but my power bills are very reasonable so i am ok with it.
  • billtwocase
    billtwocase Member Posts: 2,385
    Is it

    electrically heated? Pics would help. If it is a heat only boiler, there shouldn't be summer months consumption. That only happens when you are maintaining temp. I think you may have a tankless coil and a storage tank? 
  • Unknown
    edited February 2012
    more details

    yes, the household water is electrically heated. i don't have any questions about the hot water heater.

    the boiler is heating only - therefore unnecessary in summer months. i will turn it off altogether in may.

    last year, i did turn all thermostats off during the summer months, but didn't turn the main power to the boiler off until august when i found out it was safe to do so. even with all thermostats off, the boiler came on fairly frequently, presumably just to maintain the boiler temperature, but the amount of oil burned may through august was 320 litres / 84.5 gallons and seemed to me to be a huge waste.

    Here are a few pics. Space is tight so they aren't very good:

    In 1.jpg you can see the overall boiler set-up on the left, and the separate hot water heater on the right. In 2.jpg you see the boiler / burner, in 3.jpg I scan up so you can see the boiler and some of the valve work, and finally in 4.jpg I scan up again so you can see the expansion tank and some more valve work. (I'm wondering if the expansion tank is too big, too.)

    (Don't worry about the various rust spots you see - I already had some plumbing work done to address small leaks...)
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    Some thoughts...

    I think your boiler is oversized. It's short cycling because it's divided into 3 zones, making it even more oversized unless all 3 zones are calling for heat on the coldest days of the year.

    Some solutions:

    Control your boiler with out door reset. Lowering the boiler temp, when the outside temp is warmer, will give you longer boiler cycles. A complete control strategy--outdoor reset, zone synchronization, would also help. And you could probably benefit from a buffer tank.

    Deeper setbacks would give you longer runtimes, and theoretically better efficiency.

    Your thermostats really aren't 'synced'. What zone control are they all wired to?

    Simpler fixes could be a Beckett heat manager and/or an aquasmart control.

    Your oil consumption really doesn't appear high, and it's difficult to compare last year to this year due without adjusting for Degree Days, and the fact that you change the thermostat settings.

    Btw, heat doesn't rise, heat moves to cold. Hot air is lighter then cold air, so hot air rises.

    There was an error rendering this rich post.

  • billtwocase
    billtwocase Member Posts: 2,385
    What zone valves

    do you have? I agree that you may be oversized also. You can also down fire the unit. What nozzle size is in there now? I would also turn your low limit all the way down. Your high about 180*F.  Also all baseboards are open and heating? Any baseborads or heat source under any of the thermostats?
  • Lots of things to check out

    Many thanks to both of you sirs. Given that I have no previous experience or knowledge of this stuff, you have given me several processes/components/terms to research and test. I'll be an expert in no time! (better call the Fire Dept right now)

    Good question about heat sources near thermostats. I do need to move one thermostat as it is on the outside of one of the boiler room walls. The previous owners tried to shield it a bit with insulation and a panel behind the stat, but I really should have moved it when I replaced the thermostats last year. So this might be contributing to some of the short cycles, but its not the only reason.

    I'll get Googling and explore some of these possibilities, and I'll be back to you with more hot air (not heat).

    Many thanks!
  • Unknown
    edited February 2012
    Baseboards, thermostats, valves

    All baseboards are open and heating. About a quarter of them were replaced a year a half ago during renovations too, and the whole piping system was checked and flushed. Still bloody noisy tho. Must try to bleed them...

    The two upstairs stats are well away from heat sources, but they are only about two metres / six feet from one another. I really should move one of them a room or two away.

    Each of the three zone valves has a separate electrical box, all wired to a transformer, and then out to one of the three thermostats. Something about that feels a little bit backwards to me, but I don't know enough yet to judge for sure. The wiring is an absolute mess and could use some reorganizing anyway.

    I'll keep trying to get answers to your questions.

    Appreciate your help
This discussion has been closed.