Lochinvar Noble MRHL Lockout

BoilOver

Recently my son was taking a shower and complained that the water was cold midway through the shower. I went to my combo Lochinvar Boiler and saw that a MRHL lockout occurred. I reset it once, and same thing immediately happened. (Sounded like flash boiling sounds to my untrained ear)

As a homeowner is there anything I can quickly try to get it back operational? Reading the manual it looks like it could be either the diverter valve motor or the boiler circulator pump.

How would one isolate if in fact it is one of those parts? The circulator pump looks like something I could handle replacement on if I can get the part, less sure about the diverter valve motor.

I've got a call out to our installer, but running into availability issues at the moment.

Unit is about five years old. We've been running the radiant heat side for about a month now. this season without issue

Many thanks

GGross

You need a meter to check there is power going to the pump when there is a call for heat or DHW. if you have power then need to check the pump is actually operating. They aren't specific about checking the diverter valve, and I hate to just write off the possibility but if this happened during a call for DHW the valve was already in the correct position, there isn't much that could make that valve suddenly move halfway to block the pump, if the motor suddenly failed the valve would still be in DHW position, I suppose it is possible the board could have a defect that signaled the motor to move but even then the flow would just divert to the heating system. My initial suspicion would be an air locked pump, or failed pump, but if that didn't pan out I would be calling tech support to check the valve, there are instructions in the manual to check the water sensors to verify they are reading accurately to rule that out. do you have pictures of the install? is there a fill valve installed and is it left open? has anyone recently filled any section of the heating system or has the entire system been up and running for 5 years?

BoilOver

Thanks!

I do have a multimeter I can use, but was concerned about when to do this. It seems like I only have a few seconds on startup after a call for dhw before it locks out again. I'm guessing measure on the control board? Any concerns about causing the system to repeatedly go into high limit if it takes me a couple tries to get a measurement.

There is a fill valve in the open position. I used the prv on top of the boiler to pull water through heat exchanger after I flushed the domestic side about a month ago as part of heat startup (prob wasn't necessary), but it's been running without issue for the last month.

GGross

Flushing the DHW heat exchanger should not require opening the boiler PRV, your DHW heat exchanger and boiler heat exchanger have completely separated water. When you opened that PRV your fill valve would then add more fresh water, more fresh water adds more minerals which can cause early failure of the heat exchanger and any ferrous metal components in the system, in addition this will add a bunch more air to the system. Ideally a well installed boiler will have no leaks, the fill valve will either be closed or disconnected, and the water will never change unless the system needs service, or a glycol solution needs to be changed. if the boiler is always going back to its high limit fault, even after being manually reset, immediately after a heat call. I would shut it down, its generally not good for them to trip that limit multiple times.

My initial thought would be to purge the system of air to see if the pump is airlocked, though it may have failed. pictures would possibly help. I imagine a parts changer would jump straight to changing that pump and probably be right half the time, but still something killed the pump it's not just bad luck and my money is on air

I wonder if anyone else here knows a way to manually change the diverting valve position or run the pump via the onboard control? it would make troubleshooting much safer, possibly tech support would know a way to force the pump or valve to operate? I would think shutting power down and bringing it back on would move the valve but I'm not 100% for this model

BoilOver

Thank you very much for the reply. In good news the hvac contractor arrived this morning. Isolated to a seized boiler pump

GroundUp

If the radiant is working, the pump is not an issue. If the diverter were faulty, you simply wouldn't have hot water. It sounds like the heat exchanger is plugged and is not allowing any heat transfer. Unless of course it's piped wrong without primary/secondary, in which case it could be any of those 3 items.