New boiler - Pressure problem

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Westchester County, NY
Hi all, First time on this forum. Lots of good information. Hopefully someone can give me some advice. Here it goes, previously My house had a Slant Fin Galaxy GX-100 gas boiler with a tankless heat exchange, it ran for over 25 years without a problem until the last 2-3 years when started to leak. I know the company went Under or got acquired by another company but still went on and bought and installed this past March 2023, the newer version Galaxy GXHii-115 which was almost a direct replacement with minor pipe modifications. The contractor installed the unit, put in a new expansion tank, PRV and water inlet valve, it went through the testing process but here in NY during March and April was a bit warmer so the boiler will run very little but not like winter time, the test was probably not very complete, tested the baseboards, hot water but not sure if it needed longer time. The unit came in with the electronic control Aquastat 3200, which the installer did not have much knowledge on the programming side of it. At the beginning the hot water was not very hot So I did some reading and finally setup the low limit at 180 and high at 200 instead of default of 190. After the final setup it ran beautifully since March until last week. During this entire time the unit will to the same: the heat tubes will come on every 1 hour and 15 minutes, for about 2 minutes, it will bring the boiler to 180 then will shut off but the temp on the electronic display will keep rising to 203-206, the upper limit light will come on, it will stay there for a 45 minutes or so and eventually start to decrease, as it went down the upper limit light will go away and the will go continue to decrease to 170 which is 10 degrees below the low limit and then the process will start again.

Here is the problem: during all this time I never paid attention to the temp/pressure gauge on the side of the unit, last week I engaged the boiler for the first time and came on at 70 degrees. It ran for a short while, all baseboard heaters were hot and working, continue to run the unit for about 15 minutes, soon after the PRV started leaking water and noticed the gauge marked 30 PSI. My first inclination was the 180 -200 setup and brought down to 170-190 degrees but the unit continued to expel water though the PRV not matter the setup on the electronic controller. as I was playing with the different settings noticed the pressure go all the way down to 0 or close depending on how long the boiler recovers from the previous warning cycle. Called the installer and explained the situation, first thing he mentioned was the expansion tank which I reminded him he put a new one, the he mentioned 2 or 3 other things that could be causing the over pressurization of the unit, the second time I spoke to him then he gave other reasons, not sure if he really know of what is going on. At this time still waiting for him to show up and it is getting colder in NY. I apologize for the lengthy post but wanted to provide as much detail as possible. Any help will be greatly appreciate it.


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