Will L7224U Help diagnose my boiler cycling issues

esandma

Hi All -
I have a Weil-Mclain/Carlin oil fired burner that eventually reaches T-stat set-point but it could take 8 hours to get there on a cold day (with the furnace going on for about 6 minutes and off for about 10). Once at the set-point, it seems to hold it steadily, however. System has 3 zones (2 heat & one for hot water tank) and all zone heads appear fine. Hi limit set to 180F & lo limit to 160F with diff of 15 (if any of that matters).

I've replaced a few things that needed replacing anyway such as circ pump (it was mounted on veritcally) & Extrol tank (hadn't been replaced in a several years) and attempted to do a bit of trouble-shooting but haven't been able to resolve the issue. Also did a good cleaning w/ oil filter change.

Thinking about replacing the L8124A aquastat with a L7224U since these newer ones seem to have some diagnostic capability. Will the digital aquastat point me in the right direction or is it just a waste of time/$? I've also read that this cycling issue may be inherent in oil-fired hydronic systems. Opinions/suggestions would be appreciated?

STEVEusaPA

That control wont help diagnose. You would be better off changing to a HydroLevel or Aquasmart, to take advantage of some better technology and get low water cut-off.
When you say it takes 8 hours, are you coming off a deep overnight setback? Otherwise, something else is wrong.
I would have someone who really knows hydronics go over all the piping and the entire system.
Maybe it wasn't properly bled. Maybe the circulator is wrong/not working/installed incorrectly.
Cycling is an issue if any piece of heating equipment is oversized, or the distribution system (piping and circulators, etc.) aren't delivering the heat to the rooms.
Your cycling, especially on the coldest days sounds more like a circulation/piping issue/problem.

esandma

Hmm... there seems to be a good amount of heat coming out of the baseboards and it's pretty instantaneous once a call for heat is made. I can hear the circ pump running so I believe that's okay.
Improperly bled system is possible though I don't know how I'd check that (it has those auto air bleeders on the system). System coming from 55F (night) to 67F (day) so it's not too deep a setback.

The heating system is a retrofit from electric baseboard to hydronic and it looks like 1/2" PEX is used throughout (pulled through walls to both stories).

KC_Jones

esandma said:

Hmm... there seems to be a good amount of heat coming out of the baseboards and it's pretty instantaneous once a call for heat is made. I can hear the circ pump running so I believe that's okay.
Improperly bled system is possible though I don't know how I'd check that (it has those auto air bleeders on the system). System coming from 55F (night) to 67F (day) so it's not too deep a setback.

The heating system is a retrofit from electric baseboard to hydronic and it looks like 1/2" PEX is used throughout (pulled through walls to both stories).

That is a ridiculously deep setback and is most likely the problem. I wouldn't do more than 3-4 degrees of setback.

Is the house actually dropping to 55 at night? If so I think you need to seriously consider some air sealing which will pay you back more than any changes to the heating system.

esandma

Okay thanks -
Actually no... it might hit 59F by morning if the wind is strong (we have 5 miles of open saltmarsh on 2 sides of the house and a small sand dune buffer on 1 side, so it does get windy).
I thought that was a pretty standard setback but I guess I was wrong.

nicholas bonham-carter

Keep it at 65, and see if it maintains that. If you were going away for a few days/weeks, then a setback would save some money; however with short setbacks, a lot of fuel has to be burned just to recover.
The cycling of the boiler would indicate it would be capable of supplying more heat, but that you are at the limit of your radiation.—NBC

KC_Jones

Just a thought. Measure how much finned baseboard you have, then tell us the boiler size.

Since you are trying to come out of a deep setback, it's possible you have enough emitter to heat the house properly, but the boiler is over sized for the amount of emitter you have.

If the above is true it could explain, at least in part, the short cycling.

Jamie Hall

A bit of perspective on that setback -- which is insanely deep. On one of the properties we maintain, which is occupied, that deep a setback would take at least a day to recover from -- and the heating system is in excellent condition. The other main property we care for is set to 54 in the winter, but it is not normally occupied. If the owner decides to come, we have requested -- and they comply -- that we are given 3 days notice to bring the house up to comfort.

SeymourCates

@esandma

Your situation is quite classic for oil fired systems. You have not provided any info on the size of the boiler or the length of the baseboard in each of the zones. However, if the boiler is the typical four section and is firing at 1 gph, you have the availability of 110K BTUH to heat the baseboards. Now, let's assume that one of the zones has 70 feet of baseboard and only that one zone is calling the boiler. The zone can dump 35K BTUH. That's it. So, the boiler is going to climb very rapidly to high limit and shut itself down. This process is repeated endlessly, as you have observed.

That's the nature of oversized oil fired boilers.

Couple of things you can do:

1) Most of the boilers can be successfully downfired to 80% of rating without negatively affecting combustion efficiency. A smaller nozzle and an air adjustment with a combustion analyzer can achieve this.

2) The L7224 and the Aquasmart have the capability of setting a 30 degree differential. The L8124 gives you a fixed 10F differential (ignore the differential dial on the L8124.........it has no effect on the high limit). So, the boiler will run for 3X the time before it shuts down on limit with either of those two controls. The Aquasmart has the additional benefit of purging the boiler of heat for 4.5 minutes after the call ends. This time is really not quite sufficient but it is far better than nothing which is what the L7224 and the L8124 offer.


As has been stated, deep setbacks on oil fired systems where the radiation is just barely adequate for the design day are not desirable. In theory, the building will never recover on the design day if the radiation is perfectly sized for heatloss. The boiler cycles endlessly.

Jamie Hall

One minor comment: Mr. Cates remarks should indicate that the problems he implies are unique to oil fired boilers are, in fact, common to any fuel fired boiler which has a fixed firing rate.

There are boilers from a number of different makers which are gas fired, which can modulate the firing rate without much impact on efficiency. While this can, in principle, also be done with oil fired equipment, it is more difficult, so other approaches are used instead.

Does anyone know? Is Mr. Cates affiliated with any of the manufacturers of modulating gas fired boilers? If so, his signature should say so.

esandma

Sounds like I may have a few options.
This is a great heating forum with lots of knowledgeable people!

Thanks to everyone who responded.