Manual reset high limit tripping

Dan C.

I am trying to figure out a problem at a hotel I service. The domestic water system has two Raypak 625,000 btu copper fin boilers and 3 100 gallon storage tanks. Starting this week the manual reset high limits on both boilers are tripping intermittenty. I was there for anout two hours yesterday and everything seems to be working normal. They had no hot water again today and had to reset them. What could cause this to happen periodically?

Dan C.

One of the boilers does have a bad flow switch that needs to be replaced but the pump is working.

JUGHNE

When was the last time the heat exchanger tubes were cleaned?

ScottSecor

In my experience manual reset aquastats only trip for two reasons. 1. The operating aquastat has failed (very rare).
2. In your case there is lack of flow. Often caused by a bad circulator or a partially clogged heat exchanger.

I have seen flow switches fail, but often this is the result of the bellows leaking, not lack of flow. I suspect the flow switch needing replacement is related to a clogged heat exchanger.

EBEBRATT-Ed

raypack's are very touchy with regard to flow. Just saying the pump is running doesn't mean much. Those boilers don't hold much water so flow is everything

Zman

I agree with the above comments about flow.
Sometimes the temp spike happens when the boiler and the circ turn off. It is pretty common for a boiler like that to have a post purge relay on the circulator to lets the boiler run after the burner has shut off. I would check that as well.