Here's what i have. Burnham V7 boiler with 2 zones. One zone for baseboard heat in small 3 bedroom well insulated ranch. second zone for indirect 41 gallon amtrol hot water tank. The hot water tank was recently replaced as the old one developed a leak because the bottle had failed. I had not had the boiler cleaned/serviced since I moved into the house 3 years ago. I know I should have, but I'm a procrastinator, what can I say. I finally got an annual service contract with my oil company, and had someone out to service it. He cleaned the boiler, and did a "tune up". Had to call him back 2 weeks later, as I noticed black smoke out the chimney. Apparently, the "air vents" got bumped and were inadvertantly closed. he said I probably bumped them when I was installing my new hot water tank. That's certainly plausible, but I'm not sure why he didn't secure the set screw the first time he did it, which should have prevented them from moving if bumped. In any event, he cleaned once more and reset them. The technician did several things I did not care for. First, to run the boiler for servicing, he manually opened the zone valve on the zone for the hot water heater. As a result, he let my brand new tank get too hot, and the tank spit out an error code (it does so if water temp goes over 150). I happened to go downstairs when he did this and he asked me to look in the book to determine what the code meant. I opened the hot water on my basement sink, and let it run for a few minutes and that took care of the error. he claims he did that so he wouldn't make my house hot (was a warm day) but it struck me as dumb. The relief valve didn't blow, so I'm guessing it didn't go too much over 150, and hopefully didn't hurt anything, but still it seemed like a bad thing for a "pro" to do. Next he adjusted the dials in my aquastat. I never saw where they were set initially, but he recomended the high setting be set to 180. Seemd to make sense since I've seen the gauge on the boiler top out at 180 in the past. Well, what I didn't realize is, apparantly the high on the aquastat was initially set to 145. However, the reason why it was set so low is because my aquastat is off by 35 degrees. How do i know you ask? Because this past weekend temps dropped significantly, so I used the heat for the first time. I checked the boiler after it ran for a while, and it had spewed all over my basement through the relief valve. Temp was at 215 and pressure around 30 psi! In any event, after much testing and research, I found that it is simply a case of the aquastat not being accurate with the temp. I'm guessing either the probe isn't seated, or no gel was used on it when it was inserted. Even though it's not accurate, it's very consistent. With the high set at 145 it kicks off at 180 degrees every time. So after adjusting the aquastat the heat runs at the appropriate temps. Needless to say, the tech didn't bother to watch it cycle otherwise HE would have caught this. However, after I figured this out, I noticed it was still running very high psi. at 180 degrees, psi hit 30 and relief valve opened a little. So back to the drawing board. Likely culprit, expansion tank. Checked the air valve, and it it leaks water. So I replaced the expansion tank, and now the pressure is 12 psi cold and 19-20 psi at 180 degrees. so that's settled. Now, last night I had a fairly long call for heat. I observed the boilers performance. The temps and psi were fine. However what I'm noticing, is the boiler is hitting the high limit really fast. For example, it was probably around 40-45 degrees out and the house temp was 64. Set thermostat to 68. The boiler kicked on and ran up to the 180 high limit and shut off. Circulator kept running as it should, and once the temp dropped 10 degrees, the boiler kicked back on. This repeated several times until the house temp hit the called for 68 degrees. What i noticed is, the boiler climbed up to the high limit very quickly. average run time seemed to be around 2 minutes, give or take 10 seconds. Then just the circulator would run for several minutes while it dropped through the 10 degree differental, an dit would then repeat. Ok, finally, here are my questions: 1. Should I be concerned about the fact that my new tank was heated a bit over 150 degrees? 2. Is it dangerous to leave the aquastat as it is (set 35 degrees lower to compensate for it's innaccuracy)? Would it make more sense for me to try and see if it is just that the probe isn't seated, or should I just bite the bullet and replace it? 3. Is the fact that my boiler is running up so quick on a call for heat going to lower my efficiency? I know as part of his service, he replaced the nozzle. could it be that the old nozzle was restricted, and the new one is just flowing more oil, hence heating faster? Or, perheps he replaced the nozzle with the next size? I wouldn't think that would be done, but who knows given the other things he did. 4. Could the fact that the boiler heated so hot have caused the expansion tank failure? Expansion tank is rated to 240 degrees, but it was 8 years old. Worth noting, before the events of the past few weeks I knew almost NOTHING about how my heating system worked. I'm a pretty handy guy, but this is my first home. As frustrating as these events have been/are, at least I'm learning alot. Also, thanks to Grady and NJ Trooper. Most of my troubleshooting/learning thus far has been from reading their responses to other posts on this site.

Just installed a new pressure relief valve on my oil boiler, and after 3 days it is leaking now. The pressure in my boiler is normally around 10-15* but is hoovering around 25* now. Why is the relief valve leaking ? Why is the pressure going up ?