Lochinvar KBN500 XL dhw firing rate adjust?

wcs5050

Service and manuals seem pretty lean. Boiler is older model with touch pad. I feel like there is a back door beyond normal installer menu, but can't find anything. New 80gal SSU doesn't take enough heat away from boiler which then begins to make those bad noises. I need to turn this thing down to ~25% or so. Does anyone have a clue about this old controller beyond the 5309 installer entry? Worked until 1130p hoping to get hot water on, but I know when I'm beat.

Gary Jansen_4

Page 20 of the service manual. DHW maximum rpm limiting.

wcs5050

Noises of percolation etc as burner overcomes leaving heat from boiler. This is the model from ~6 years ago... Where new control allows for deration, old control appears not to. This really sucks. Need tech support and had to happen on a weekend. I wonder if PC interface would access more parameters. I vaguely recall that it's possible to upgrade to current control. Last thing I tried before leaving was bringing boiler DHW supply temp down to 125 to see if it would slow itself. It still behaved unsmoothly.

wcs5050

Lochinvar and manf rep made it clear DHW burner derate feature not available on 1st gen boiler/control....just wasn't offered, but they say it's not obsolete. Need to add mass to dhw loop somehow...low loss header(anyone ever built their own?) or buffer tank.

Mark Eatherton

Has been a while since I've worked on one of these, but if memory serves me correctly, they have 2 options for doing DHW. One is a switch (aquastat) and the other is a 10 K sensor. By using the 10 K sensor versus an aquastat, the control can "see" rate of rise and tank approach temperature. This will allow the burner to begin cycling back faster. With the switch, it can't "see" what is going on and runs full throttle to the high limit. Kinda like running a truck into a brick wall at full throttle... BAMM. I also remember that when you did connect to the PC port, that those parameters were shown, but grayed out.

Occasionally, they can program a new control board that gives a little more flexibility, but you are already driving a tack with a sledge hammer.

I know some people are going to say this is a stupid suggestion, but if you go with a larger reverse indirect, it will make some difference, especially during peak loading. And use a sensor instead of an aquastat.

It (500K btuH) is really a misapplication. I'd have split the load between two boilers if in fact the space load is that big.

Their control logic is one of the best I've seen on the market. With proper training, and using their PC interface you have the ability to make it stand on its head and spit wooden nickels... Plus you can do data logging to diagnose intermittent problems.

ME