Boiler cycle

Our new burnham 206h boiler seems to turn on and off sometimes every 4-5 minutes. Not from themostat claa but from the high limit switch. Can you guys start directing me into what this might be, or what other info I can provide to diagnose. We had a heat loss done. The differential between the supply and return when the boiler gets up to temp is about 18-19 degrees. Yet its seems as though it cools down pretty as the circulator keeps moving it. Too small a boiler? Too many convectors? Too much piping? The house has 19 convectors, in monoflo style design. It is one zone right now. In the spring it will be further zoned out. It was also suggested that for this year the larger red B & G 100 pump be used instead of the 007 which came with it.

 

To see a boiler cycle when you are at other than design temperature is perfectly normal. The boiler is making heat faster than the radiation (convectors) can get rid of it.

 

And the differential between the supply and return is right on target, so changing the pump would likely do nothing for you... don't bother.

The question to ask is this:

Is the house heating evenly ? Comfortable in all the rooms ?

If so, relax... enjoy your new heating system.

 

Don't forget, your heat loss only means your boiler is close to being properly sized for only the coldest design day of the year! Most of the other times it is over sized, and some cycling will be normal.

Pete

 

Grady,

I follow your comment, but in my case it cycles from the 180 degree high limit down to I think it has a 15 degree differential. So wouldn't that mean the convectors are getting rid of it pretty fast? Maybe the pumps is too big?

 

No. The 20° difference you are seeing between the supply and the return is EXACTLY right. The pump is the right size.

Is the home heating nicely all around ?

Relax... everything is fine. It's doing exactly what it's designed to do.

 

If you want to change the cycling you could try a Beckett Heat Manager. It would change the differential automatically as it learns the system.

 

trooper the house heats nice, the cycling is somewhat of a concern because of the heat bill.

 

Does your boiler make hot water or did you have a indirect hot water tank installed? If you have a tankless coil then that could be your cycling issue.

 

johny2050 no it does not

 

If ALL of the following conditions were met, the boiler would stay on. But if ANY are not met it is going to cycle as you describe:

1. The boiler is sized for the heat loss of the house.
2. The convectors & heat from the pipes match the heat loss of the house AND the capacity of the boiler.
3. The outdoor temperature is the same as design temperature.

One very nice feature which increases efficientcy of the modulating/condensing (mod-con) boilers is their ability to vary the firing rate based on outdoor temperature.

Does your boiler ever fire when there is no call for heat?

 

If the the thermostat keeps calling, but the boiler cycles because it hits the high limit of 180 degrees, does it mean that my convectors are pulling the heat out very fast, and that's why i get a 5-6 minute cycle on the high limit?

Also the Burnham manual does not state what the differential is on the high limit. I assume it is 15 degrees, as i have not watch the tempurature guage to see yet. I believe it is a 4008 honeywell that came with the Burnham.

Someone brought up a heat manager, but would the taco aquastat which works with the taco zone panel be a better choice?