Need advice before calling the plumber back. Boiler with indirect dhw.

Gumby77

So here the issue, I'll try to be as concise as possible:

New Knight 80,000btu boiler installed and have been having issues with heating and DHW. Some of the symptoms are:

1: Lets say the DHW tank is at set point and the SH thermostat calls for heat the boiler will turn on and within about 5 minutes the DHW tank will have dropped to the point it calls for heat without any hot water being used. This overrides the SH call and heats the DHW to setpoint then the boiler goes back to satisfying the SH call. I think this process repeats if it takes long enough to satisfy the SH call for heat.

2: I had a call for heat today and the outdoor reset said it was 28F and called for a set temp of (106). The boiler fired and hit the set temp (output temp was 107, system temp was 99) and modulated down and the set temp kept going up and the boiler shut off but the thermostat was still calling for heat. I thought that was odd and I checked to see if the system pump was on and it was off... I looked on the display and it said Boiler pump off, System pump on and DHW pump off. I checked the boiler pump and it was on when the display said it was off, now I'm 75% sure I know what pump is which. Is it possible the pumps are wired incorrectly causing some problems?

I had the same installer come back earlier to fix an issue with the system temp probe because it wasn't in contact with the pipe and not insulated causing a big discrepancy in outlet temp vs system temp.

I'm not sure where to start the troubleshooting but I hope I have gave enough info to spur further questions.

Pictures attached.

Leon82

After the thermostat shuts off the heat call the system pump will run for 2 minutes default of I recall.

I don't remember but there are probably settings for dhw priority and the time limit before the boiler resumes space heating

Zman

Problem 1 sounds like a lack of check valves in the boiler and DHW circs. It is pulling heat out of the water heater during heat call.

Problem 2 sounds like normal operation. Please elaborate.

Leon82

I may be thinking of the primary pump

Ironman

A couple of things to check:
1. Make sure the pumps are wired and programmed so that only the DHW pump runs during a domestic call and that only the boiler and system pump run during a space heating call.
2. Make sure there are check valves installed in each pump and that's none of them is stuck open.

The system circulator is installed wrong: it MUST have the motor horizontal, not vertical. It will fail in that position.

Gumby77

Leon82 said:

After the thermostat shuts off the heat call the system pump will run for 2 minutes default of I recall.



I don't remember but there are probably settings for dhw priority and the time limit before the boiler resumes space heating

Thing is the thermostat was on and the boiler had exceeded its setpoint and shut off. The display said boiler pump off and it was on and said system pump on and it was off.

Gumby77

Zman said:

Problem 1 sounds like a lack of check valves in the boiler and DHW circs. It is pulling heat out of the water heater during heat call.

Problem 2 sounds like normal operation. Please elaborate.

There is supposed to be check valves in these pumps and even if there was the way it's piped (see picture) I think it's pulling the DHW tank temp down because the SH call setpoint is lower than the temp in the DHW tank and pulling it's temp down, now if it got cold enough outside to have SH setpoint higher than 130F (DHW setpoint) then it would actually heat the water up higher and cause scalding concerns.

Problem 2 is the an issue because it says boiler pump is off when it's really on and says system pump is on when it's really off.

I might call Lochnivar and talk to them next week too.

Gumby77

Ironman said:

A couple of things to check:
1. Make sure the pumps are wired and programmed so that only the DHW pump runs during a domestic call and that only the boiler and system pump run during a space heating call.
2. Make sure there are check valves installed in each pump and that's none of them is stuck open.

The system circulator is installed wrong: it MUST have the motor horizontal, not vertical. It will fail in that position.

I'll have to check on the DHW call and see what pump is running, I think I remember that the boiler pump runs too.

I'm guessing the only way water can get to DHW tank during SH call is if the check valve in the DHW pump is bad (like you said) and cooler water is coming through that after passing through the boiler pump.

I'm sorry I forgot to mention this is an old picture. I called them back to fix the system temp probe and the pump orientation, which was easy because the webstone valves have a rotating flange.

kalex1114

default setting for pump to run after set point is met is 30 seconds. When thermostat is calling for heat and boiler shuts off does it go into anti-cycling blocking? it should say on the display. after blocking time expires it will refire and keep going at low modulation. For point 2 i have similar issue. When you are using system probe it becomes the control point instead of outlet. So if your outlet is at 107 and system at 99 it will keep going up until it reaches 106. By that time your outlet will run hotter and then as system temp approaches 106 it will overshoot too because lochinvars are slow to modulate down. Then your offset will kick in and it might get blocked again. Check out my lochinvar thread if you want

kalex1114

Also system probe should be after the pump not before it i think its in the install manual.

Are you running dhw at 130f? That's not idea. You want DHW call to finish as soon as possible instead of at lower temps. Mine is set for 187f with 3f offset. My call is usually done in about 8-12 minutes. That's going to 65 gallon indirect.

Gumby77

> @kalex1114 said:
> Also system probe should be after the pump not before it i think its in the install manual.
>
> Are you running dhw at 130f? That's not idea. You want DHW call to finish as soon as possible instead of at lower temps. Mine is set for 187f with 3f offset. My call is usually done in about 8-12 minutes. That's going to 65 gallon indirect.

The DHW tank thermostat is130F with a boiler set point of 165F.

Ironman

Gumby77 said:

Zman said:

Problem 1 sounds like a lack of check valves in the boiler and DHW circs. It is pulling heat out of the water heater during heat call.

Problem 2 sounds like normal operation. Please elaborate.

There is supposed to be check valves in these pumps and even if there was the way it's piped (see picture) I think it's pulling the DHW tank temp down because the SH call setpoint is lower than the temp in the DHW tank and pulling it's temp down, now if it got cold enough outside to have SH setpoint higher than 130F (DHW setpoint) then it would actually heat the water up higher and cause scalding concerns.



I might call Lochnivar and talk to them next week too.

A DHW call has priority for up to 60 minutes (depending on the setting). During that time, the system and boiler circs should be held off and the boiler will target 180* SWT to heat the indirect as quickly as possible. The ODR target temp is overridden during this call. Once the call is satisfied, the boiler will return to space heating and stop the domestic charging circ. In other words, the ODR target temp has no effect on a domestic call. That's assuming your setting are correct.

Gumby77

> @kalex1114 said:
> default setting for pump to run after set point is met is 30 seconds. When thermostat is calling for heat and boiler shuts off does it go into anti-cycling blocking? it should say on the display. after blocking time expires it will refire and keep going at low modulation. For point 2 i have similar issue. When you are using system probe it becomes the control point instead of outlet. So if your outlet is at 107 and system at 99 it will keep going up until it reaches 106. By that time your outlet will run hotter and then as system temp approaches 106 it will overshoot too because lochinvars are slow to modulate down. Then your offset will kick in and it might get blocked again. Check out my lochinvar thread if you want

It's hard to explain what's happening and that's probably my fault haha. I'm not exactly sure what's happens because I am not there to see it. Usually I see the vent not putting out vapor and go and look at the thermostat and it's calling for heat, then I'll go downstairs and check the boiler and it says setpoint met and isn't running and isn't in standby and still has the little house icon with the 1 in it for zone 1 thermostat calling for heat. That's when I checked the pumps and found the boiler pump running and the system pump off which is exactly the opposite of what the display on the boiler says. That's what led me to think the pumps are wired wrong. Can you look at the picture and reassure me I have the pumps labeled correctly?

Ironman

They are. But again, they may be wire reverse at the boiler.

Leon82

If you are somewhat handy you can remove the sheet metal covering the wires with a Philips screwdriver to see where the wire from the circulator goes.

Gumby77

> @Ironman said:
>
> A DHW call has priority for up to 60 minutes (depending on the setting). During that time, the system and boiler circs should be held off and the boiler will target 180* SWT to heat the indirect as quickly as possible. The ODR target temp is overridden during this call. Once the call is satisfied, the boiler will return to space heating and stop the domestic charging circ. In other words, the ODR target temp has no effect on a domestic call. That's assuming your setting are correct.

That's pretty much how mine works except I have the DHW target is 165 vs 180 ( maybe I'll change that). Problem is the DHW always calls for heat at least twice during the SH calls even if not using hot water.

Ironman

Sounds like the issue is with the pumps: wired or programmed wrong; stuck check valve.

Brewbeer

I have a Lochinvar and when it was first installed, while in CH mode it would pull heat out of the indirect tank, causing it to cycle between CH and HW modes every 30 minutes. Problem solved when a flow check was cut into the HW loop.

Leon82

On a side note I don't remember if pex is rated for uv but you may want to block the light from entering the window

Gumby77

> @Leon82 said:
> If you are somewhat handy you can remove the sheet metal covering the wires with a Philips screwdriver to see where the wire from the circulator goes.

I feel I'm pretty handy and I can do that in the am tomorrow. Just wanted to make sure I had the pump identified correctly. I suppose there's not a way to check the valve without pulling the pump is there?

Gumby77

> @Brewbeer said:
> I have a Lochinvar and when it was first installed, while in CH mode it would pull heat out of the indirect tank, causing it to cycle between CH and HW modes every 30 minutes. Problem solved when a flow check was cut into the HW loop.

Sounds about right, I bet the valve built into the pump is bad.

Leon82

Not really., The ifc flow check is a little plastic piece that pops into the Id of the flange

kalex1114

You should increase dhw to at least 180 so that it can heat up as fast as possible. If you happen to catch the heating call then you can watch the screen for the entire time and see what is happening. I did it few times and its easy to see. Also check your ODR curve and see what it set to at low and high temps.

Leon82

You have the webstone flanges so checking isn't that big of a project.