What is causing new Gas Boiler to turn on and off

[Clarence Martinn]

Got a new Lennox Gas Boiler installed, and after many hiccups with it, It finally was running good..

Now the problem.


The electronic thermostat on the wall is set at 70 Degrees from 8 am to 11 PM. After 11 PM, the Thermostat is set to 68 Degrees. During either set temp, once it reached 68 at night or 70 during the day. The temperature in the house stays at that temp. That's a good thing.

The part I don't get, is why the Boiler turns on every 5 to 6 minutes , when the Temperature on the wall thermostat did not go below either 68 or 70 Degrees ?

One thing I did notice, when I went in the Basement to check the Boiler, that Temperature gauge on the Boiler would go down after the boiler shut off. That is understandable. But, even if the water temp in the Boiler went down to , say 80 Degrees, for example; if the room temp that the wall thermostat reads does not drop below what it was set at; why would the Boiler fire up ?

[Myk Rian]

But, even if the water temp in the Boiler went down to , say 80 Degrees, for example; if the room temp that the wall thermostat reads does not drop below what it was set at; why would the Boiler fire up ?

Because the heated water needs to be hotter than the room temperature. The boiler is maintaining the ideal water temp.

[Robert LaPlaca]

Assuming that your boiler doesn’t do double duty as a heat source for domestic hot water, I am going to say it sounds like it is configured kind of strange to me. I wouldn’t imagine that there is any need for the boiler to fire up and heat water if not being called by the thermostat.

[Clarence Martinn]

Because the heated water needs to be hotter than the room temperature. The boiler is maintaining the ideal water temp.

But isn't it the wall thermostat that regulates when the Boiler starts up ? When I had my old Dunkirk Boiler, the old wall thermostat, which I still have, would turn the Boiler on at 68 or 69 Degrees , and turn off when it reach 70 or 71. Is it the new Boiler or the new Thermostat that regulates things differently ?

[Clarence Martinn]

Not heating hot water with the Gas Boiler. Would like to have an indirect water heater. But, not in the budget right now. Just heating the house . One Thermostat.

[Adam Herman]

there should be an adjustment for dwell on your thermostat, this should be set for more time. it adjusts how much temperature change it takes to trip the relay.

[Doug Garson]

I suspect the boiler controls are designed to maintain a boiler water set point so when the thermostat calls for heat the hot water is immediately available. The room thermostats turn on the circulation pumps and opens the flow control valves when the room temperature falls below the thermostat set point. This is just a guess, have you asked the installer?

[Malcolm McLeod]

But isn't it the wall thermostat that regulates when the Boiler starts up ? When I had my old Dunkirk Boiler, the old wall thermostat, which I still have, would turn the Boiler on at 68 or 69 Degrees , and turn off when it reach 70 or 71. Is it the new Boiler or the new Thermostat that regulates things differently ?

I would think the old system was just a simple relay on/off control. It was (probably) either off, or at 100% hi-fire fryin-bacon ON! And nothing in between.

If the new unit has a nice display and lots of electronical-esque parameters, I'd say its a modulating unit. If so, it may very well fire more often, but the controls will only output enough 'fire' to maintain the water temperature at SP. Then the room TStat will control the pump. So said the guy in Texas, who's never owned one (but works on industrial controls).

If you want way too much theory on this, giggle a search for "PID control" (Proportional-Integral-Derivative).

[John Terefenko]

there should be an adjustment for dwell on your thermostat, this should be set for more time. it adjusts how much temperature change it takes to trip the relay.

This is what I need to do. My thermostat controls both heat and air conditioning and it comes on or off exactly one degree one way or other. Cycles too much for me. Just had air put in last year and they changed the stat. Was going to have them look at this when they come out to start and check air conditioner up for season.

[Lee Schierer]

I suspect the boiler controls are designed to maintain a boiler water set point so when the thermostat calls for heat the hot water is immediately available. The room thermostats turn on the circulation pumps and opens the flow control valves when the room temperature falls below the thermostat set point. This is just a guess, have you asked the installer?

Exactly what I was going to say. There is a loop in the boiler that is maintained at the operating temperature so that when a zone wants heat there is hot water available for that zone. Ordinarily it should not cycle as often as it seems to be unless there is cold water from one of the zones leaking back into the boiler loop due to a missing or stuck check valve in one of the recirculating pumps. If a check valve is missing, the colder water in the zone will gravity feed back into the boiler, causing the boiler loop to drop in temp and the boiler thinks it needs to heat back up again. You need to call your installer and explain the problem.

We had a similar problem in our church where one of the upper floors stayed too warm no matter what the thermostat was set at. The pump for that zone had no check vavle.

[Clarence Martinn]

That old red flow control valve above the Boiler, was part of the original piping when they had a Coal fired Boiler from the early 1900's to around 1960. When they got rid of the Coal Boiler, they replaced it with a Gas Boiler. That was eventually replaced with a Dunkirk Boiler back around 1993 ?? I think. That lasted until we replaced it with the new Lennox Boiler. Through all the changes in Boilers , that red Flo Control Valve has remained in place. They did have an old indirect water Heater that was heated off of the old Coal Boiler. They got rid of that back around 61 or 63 , when they installed State Gas Water Heaters.

As for Zones, the Boiler just heats the 1st floor. The big old American Radiators from 1920, are all piped in through one system. Turn the Boiler on, and every room heats up the same. No Separate zones for individual rooms. The Flo Control Valve was left permanently open, after we went through 3 circulator pumps. Have not burned out a Circulator pump since leaving the Flo Control Valve in the permanent open position. As for the Flo Control Valve. It's close to, if not 100 years old. House built in 1870

[Bill Steineke]

Clarence - can you tell us more about which model Lennox Boiler you have? Many new boilers - in addition to being modulating boilers. Just because the boiler is firing, if it is a modulating boiler, it may not be firing anywhere near the full rated output. Some have turndown ratios of 10:1. The concept being that the boiler will only produce exactly as much heat as is required.

Also, many new boilers (modulating or not) have integrated controls that can be relatively sophisticated. One feature that has become more common (formerly only in high-end systems) is "outdoor reset" - this incorporates an outdoor temperature sensor and depending on the control can also fire the boiler to keep the zone temperature constant.

But your installation may not incorporate any of those features, in which case it would appear that it is wired to maintain a target loop temperature and that may actually have finer resolution that your room thermostat. Your old-school massive radiators serve to store heat quite effectively and the room temperature may remain more constant than the temperature of the water that is circulating in your loop.

Just a few observations that I thought I'd share. With more information, we can pin it down more. First time post on Sawmillcreek after years of lurking - I hope I added value to this discussion.