My thermostat is set at 68. The boiler (Hot water) kicks on when needed. The problem is that it will turn off before it gets to the set degree, for a few minutes. Then it turns back on and continues to the set degree. Why is this and is it supposed to do this? Could it have anything to do with the High limit switch? If so, what can I do about it? I have the round thermostat, manual with Mercury in it.

Sounds like the heat anticipator in the thermost is set wrong. Measure the amperage from W to R at the thermostat with the thermostat disconnected. Say it is .65 amps. Just under the cover is a small slider that says longer with an arrow and numbers, set the pointer to .65

Good luck

Ok sounds like a plan, but I am not too electrically inclined. SO a walk through would be appreciated. I have a DMT7 digital multimeter. It has a bunch of numbers, letters and symbols that it can be set to. And, yep you guessed it, I have no idea how to use it. Also, you say measure W to R. Is that the themostat wire or actually on the thermostat? I do know where the small slider and numbers are on the thermo like you said. Thanks again for any input.

Northern Heat gave you a good answer to a question I didn't even try to. In another thread, he said he would be gone, so I will try to help you use it. To measure amps, look for a position labeled A or mA. MA is milliamps, 0.65 amps would be 650 mA. Turn the pointer to it. If the meter has more than 2 places to plug in the leads, select Com and one labeled A.

The next step will be easier if you have 4 hands or little alligator clips to snap on the leads. Remove the white or red wire from the thermostat. Connect one lead to the wire you removed, and the other to its terminal. Then turn the thermostat to heat and read the meter.

If your meter doesn't match my directions, try to tell me what it does have.

What number is the heat anticipator set at now? If this is a simple boiler without a control board, just find the amp rating on the gas valve, and add .05 amps for voltage drop in thermostat wire, (if over 30' long) set the anticipator to this number.

Well I appreciate the help Heat and Lab. I tried to do what Lab told me, the only problem is I can't have a wire NOT hooked up to the thermostat and still attach the thermostat to the wall to do the test with the multimeter. I did however look at the gas valve stuff like Heat suggested. I "think" I have it right. It says Total Current .5 A. So I set the anticipator to the line between the numbers .5 and .6. So I will see what that does. Also, I have a hot water low pressure Boiler by Burnham-Model #P-205A-WNV. I read Heats post about giving the most info a person can to help with questions. The thermostat is a Honeywell (round) manual one. Thanks again for your time.

Ok well I have done that and all is well. I still have the boiler shutting down though. Maybe I should clarify a little more to the problem. I set the thermostat to 66 while I am gone. I come home and turn it up to 68. The boiler will run for about 15 minutes and then shut down. The temperature will not be 68 yet. Then after about 4-5 minutes, the boiler turns back on for about 15 more minutes. Then shuts back off. It does this until the desired temperature is achieved. Once the temperature is hit, the boiler seems to run pretty normally. Is it the thermostat or is the boiler getting too hot and shuts itself off to cool down awhile or what? I have heard there is a high limit switch, could this have anything to do with this problem? Or is this how a boiler is supposed to operate? It is a Burnham 205A model. I just cycled it to see the numbers and I have 180 degree water temp. and 22PSI when it shuts down. The boiler ran for 17 minutes before it reached this.

Ok well I have done that and all is well. I still have the boiler shutting down though. Maybe I should clarify a little more to the problem. I set the thermostat to 66 while I am gone. I come home and turn it up to 68. The boiler will run for about 15 mins and then shut down. The temperature will not be 68 yet. Then after about 4-5 mins, the boiler turns back on for about 15 more mins. Then shuts back off. It does this until the desired temperature is achieved. Once the temperature is hit, the boiler seems to run pretty normally. Is it the thermostat or is the boiler getting too hot and shuts itself off to cool down awhile or what? I have heard there is a high limit switch, could this have anything to do with this problem? Or is this how a boiler is supposed to operate? It is a Burnham 205A model. I just cycled it to see the numbers and I have 180 degree water temp. and 22PSI when it shuts down. The boiler ran for 17 mins before it reached this.
OK, now it sounds like the limit is shutting it down because the water reached temperature. It will take a while for the heat to radiate from the radiators to heat the room. The limits may be set to low. In the area I live you must have 2 limits, one comes with the furnace and one we install. I usually set the factory main limit at 190-200 degrees and the strap on limit at 180 degrees.

Is this something I can check and change if necessary myself and how does it get done, or do I need to hire a qualified person? Thanks Heat!!

Is this something I can check and change if necessary myself and how does it get done, or do I need to hire a qualified person? Thanks Heat!!!

It may be nothing to worry about. Boilers always take a while to heat a house up. They just aren't as fast as forced air. As long as the pump stays running and the house gets up to the desired temperature, the gas valve cycling is no problem, all older boilers as they say, run on limit.

Ok That sounds good to me. Thanks for all your help and hopefully I don't have any more Boiler questions for a while.