Lochinvar NKC150N - DHW High Temp Issue

oltjondyli

Hi,

I have 2 Lochinvar Combi Boiler NKC150 N installed in my house, each of them with 2 zones.

I have issue with heating where the DHW in one boiler is going to high ( 170-175 degree when the DHW set temp is 125 and the DHW Max Temp is 130 ) and of course the house is not getting warm enough. More colder is outside more "cold the house is" !

In this boiler, that heat the 1st floor is biggest issue ( this part of house need more heating because is more expossed to cold). Here the water flow at pumps is always 3GPM ( and sometimes lower) in both zones.

To many times the boiler "Lockout" because is overheating.

When I open the shower/kitchen/sink hot water I can see that water temp is to high and in that moment the DHW on boiler go down, even 58-60 degrees.

The 2nd boiler, that heat the 2nd and 3rd floor (need little less heating because is less exposed from cold) the DHW is getting more higher than set temp but nothing crazy, max 145 degree. At both pumps of this boiler the GPM is going up and down from 4GPM to 3GPM.

The water line go first at 1st boiler that pumps show always 3GPM and has bigger issues with DHW and after connecting with the boiler that pumpw show 4GPM ( I don't think is water presure from system I mean).

I replaced diverter valve and the flow sensoe but the issue is the same.

I realized this issue only 2-3 weeks ago when it was extremely cold and not sure, when "it started".

I am trying to find a solution but not sure what is causing this.

Thank you,

GroundUp

Have you called tech support? If the unit is still firing on constant DHW call when that far above DHW setpoint, there is most likely an issue with either the diverter, flow sensor, or the control board. If the flow is very low or is fluctuating, it may simply be unable to react fast enough. With that said, the factory HL is set much higher than that so it should not be kicking out on ARHL until 190*+. Looks like you have a multitude of issues here but finding out what the actual flow is while this is occurring might help narrow things down. If, for example, you have a shower and sink both running wide open hot at the same time, does this same thing still happen or only when the faucet is on by itself? Space heating will be turned off while there is a call for DHW, so that may be a part of your cold house problem too.

oltjondyli

I called Lochinvar support and they sugested to replace Diverter Valve and Flow Sensor. Just replaced those but same issue. Meantime I am waiting my contractor to come and check it.

My boilers have almost 2 years installed and this started only 3-4 weeks ago, when was really to cold, before I didn't realized anything and heating was fine. Maybe issue was but I was not feeling it.

One day before plumber replaced heating and water piper in basement, I am doing finish it and he replaced those and installed new ones inside walls and beams, boilers he only shut down and turned onn when he finished. Not sure if something happened that day "or was just casuality that was very cold next day and this happened". We followed all the pipes and they looks good, not mixed heating with dhw pipes.

Shower, sink, in same time? Didn't understood this. DHW is high all the time, more I set up the Heating Temperature more the DHW go up.

When I open 1 tab, doesn't matter, shower, kitchen or sink than the DHW temperature in boiler go down, I think because inside "pipes is heating water and when open the tap its goes out".

Thank you,

hot_rod

which mode are you running for DHW?

I think in that model you can run cold start which takes longer to get hot water, or the always hot mode, where the boiler always maintains temperature

Could the dhw settings have been changed? Or reset was hit and they went back to factory default settings

I write down all the settings in the manual as I input them. Maybe just run through all of the parameters again

Alan (California Radiant) Forbes

From your screen shots, the DHW icon is not lit up which means there's no call for DHW, but it's still high DHW temperatures at your faucet. Something is screwy.

Does the red light on top of the flow sensor turn on when you turn on a hot water faucet and then go out when you turn the faucet off?

oltjondyli

Hot_Rod , settings are all set I believe, because I set those over the phone with Lochinvar assistence guy, DHW is 125 and Max DHW is 130 , i set the temp for cold days and warm days also. I also set the DHW temp on 60 ( lowest possible) and still the temp there go very high. I open the hot water tap in that moment and after hot water in pipes went off, no more hot water was coming on, only cold ( normaly this, because the set temp for DHW was 60). Maybe is something at controll panel/electric controll panel thats wrong, and this happened from electric, we shut down and turn on boiler to many times and "maybe shut down electricial without turning off boiler".

Alan,

I just tried that and I don't see any light going on or off at Flow Sensor. Sure that is light in top of the flue wsensor?! I replaced that yesterday, same with diverter valve.

The only light that goes onn when I open hot water faucet is a light down in boiler that its goes off when I close the hot water faucet. Maybe is light that show "boiler is running". I did photo when the faucet was open.

Thank you,

GroundUp

The DHW is only heated when there is a call for DHW. Water temp when there is a thermostat call for space heating is irrelevant to the DHW temp. A sink will have less flow than the sink and shower together, so if you turn off the thermostats and open just a sink versus the sink and shower together, what happens? If somebody was messing with the space heating piping, it's probably airlocked which is what's causing the high limits and cold air temp. There isn't anything wrong with the boiler, if that's the case. The flow sensor is down on the exchanger at the bottom under that steel bracket, not the temp sensor you show in the first photo at the top- just FYI.