I'm a homeowner who's been struggling with the MRHL/ARHL issues on my Lochinvar Knight KBN-106 boiler since we got the house last year. I live in the Boston area so as the weather is getting colder and more demand for heat I've been having lockouts on a daily basis. Summer months are fine as there is only DHW demand lockouts only happen occasionally in the summer time.The boiler is connected to 4 circulation pumps. 3 for space heating and one for indirect hot water tank. I've drawn and attached a piping diagram for reference. I'm also including some photos and a video of one of the lockout situations.
At first the lockouts seemed random, but lately I've been trying to see under what conditions the lockout happen. I'm still not sure if its a specific thing but it seems that when there is a call for DHW it happens the most. What happens in a typical situation is that there will be a SH call and a DHW call comes. The boiler will switch over to DHW, but as its firing (typically at 100%) and trying to get up to the setpoint temperature, before it reached it will stop firing and there is some kind of noise in the boiler (can be heard on the video starts at 52 second mark) and the outlet temperature will spike up past the high limit and the lockout will occur. It seems that before the water reaches the setpoint (160) there is a surge of how water from somewhere that comes in and trips the high limit. Limits are set to 200 for ARHL and 210 for MRHL.
In certain occasions where there is no SH calls and boiler is in standby mode and the DHW call comes by itself it will modulate properly and not trim the ARHL/MRHL limits. However this is not always the case. At times it trips the high limit even if its only a DHW call. That's why I cant figure out the exact reason why it might be tripping since it seems somewhat random. I believe the main issue is that surge of how water coming form somewhere which increases the outlet temperature and trips the hi limit sensor.
Any ideas why this might be happening? Does the piping seem ok?
HERE IS THE LINK TO THE VIDEO streamable.com/sckml