Therm on Gas boiler

[Deleted User]

Hi, my gas boiler is cycling on and off well. When it is heating the temp on the gauge located on the front of the boiler goes up to 230 degress F before it shuts off. I looked at the thermostat located on the front of the boiler and I'm a little confused. I have a link below to a fuzzy picture (my digital cam is not so good) showing the thermostat. It has a temp range painted on the right hand side and two brass circular disks with a little tab to show where its located on the temp scale. The "front" disk can be adjusted via screwdriver and its at about 170-180 degrees and the "back" disk is locked in place by a tamper proof screw (I think this is the safety shut off limit) it looks like its set around 230 degrees on the scale. So, I dont know if the gage on the front is reading wrong and its not really going to 230 or if the thermostat is bad and its reaching the danger temp and thats cycling off. I should add that the pressure is ok. How can I debug the thermostat? Thank you in advance.

http://www.thawa.net/gallery/albums/album152/IM000777.jpg

Mike

Dale

Check actual

I think you might want to check the outlet pipe temp to see if it is actually 230. If it is and this problem just started then the aquastat portion of the contol is bad and the entire control needs to be replaced. This assumes you haven't rewired anything or adjusted anything. A boiler bumping limit is dangerous and needs fixing very soon.

[Deleted User]

OK update here. I borrowed a digital thermometer from work and checked the actual temp of the unit right at the pipe that feeds the BOV (pressure relief valve ) and found that the analog gage on the front of the boiler is off by at leaste 20 degrees in the possotive direction. It was only going up to about 200-210 degrees when cycling. I also saw that it looks like there is a knob missing on the thermostat controler where you can adjust "limit control" thats the white blob on the left side of the black box in the blurry pic. Anyway I played with the only thing that I was able to adjust on there and noticed that the disk thing that was pointing at the 180 degrees controled when the unit fires. It seemed to be the starting point for the burn. I set it to 150 degrees at which point when it cooled down it fired right around my measured value of 150 and shut off right at 175 so I gather that the knob that was taken off adjusts the "burn time" which must be set at 25degrees instead of there being two disks to set a high and low you set the low and tell it how much to rise. I normally set the house themr to 60 degrees because i'm not living there and jack it up when I show up to work on the place. With the temp set like I have it now it was cycling on and off and the temp was not really going up, maybe like 1 degree in a half hour or so. I may have to jack it up a little or something to get it to heat faster. What do you think?