Lochinvar Knight MRHL Lockout

Vinny_5

Hello all, new to the board. There seems to be many very knowledgable heating pros on this board, so I was hoping to get some expert advice on an issue I am dealing with. I will appreciate any input on this matter. I am not very knowledgable when it comes to mod/con boilers, so please forgive my ignorance.

I had a wall mounted Lochinvar Knight WHN155 installed in late August last year, replacing a 79% efficiency Dunkirk cast iron boiler. My system consists of 2 zones of hot water baseboard heat and an indirect Amtrol water heater, which is controlled by a knob on the tank itself . So far the gas savings have been outstanding, but it also has been very mild here. The issue I have been dealing with is the system has had a few lockouts for the ARHL/MRHL, the latest occuring this morning when I woke up and the house was 60 degrees. Apparently the MRHL lockout occurred last night at 8:45 PM and it was in the teens overnight here. I had the installer out twice for this issue, both times they bled it feeling it may be air trapped in the lines. The 2nd time he came out, he spent much time on the phone with Lochinvar support and followed their instructions which was the same as the manual. They asked him to adjust the setpoint of the auto and manual reset limits to 200 and 210 respectively, just as stated in the manual but it would not go over 195 and 200 respectively, so it was kept at that limit. (They admitted there was a typo in their manual). I have had it happen about 5 times now in total, so after reading the manual over and over, the only thing I felt I could do to correct the issue since I was unable to raise the reset high limits was to lower the SH1 and SH2 setpoints to 170 degrees from their 180 degree settings, which I did for about a month and haven't noticed a difference in comfort and haven't had any lockouts since. That being said, last week I experimented and adjusted the setpoints back up to 180, and kept the offset at it's default of 10 degrees, and had the lockout occur again. I understand my baseboard system is meant to run at 180 degrees, so that's why I am experimenting and trying to keep it as close to that number without overshooting the limit. I was thinking of lowering the offsets to 5 degrees or less to try and keep the limit lower. I also understand that the boiler is more efficient if the return water is cooler as well and I don't notice and difference in comfort, so I was wondering if i should just lower the setpoints further. I apologize for the long drawn out first post, but I am trying to explain what I am dealing with in the best manner that I know how.

Thank you for any input, Vinny.

Zman

Outdoor reset

Vinny,

I am not familiar with the details of the knight controls. I do know that high limit problems can often be fixed by setting up a pump "post purge".



I do not believe your boiler should ever be running at 180 degrees. Perhaps you will need that much temperature to make domestic water but probably never for heat. Your boiler is already set up for outdoor reset. Assuming the outdoor sensor is installed, you just need to program it and start saving even more. You bought a condensing boiler for it's efficiency and to maximize it's efficiency it must condense. Check out the attached Ashrea document and this study someone recently posted here. http://www.bnl.gov/isd/documents/28709.pdf

Vinny_5

Thanks

I appreciate the input.  I do have an outdoor reset, and find that the unit modulates quite often which is why I have seen a nice decrease in gas usage.  I had a Beckett Heat Manager installed on my old cast iron boiler about 6 years ago, which saw my usage drop a bit, but nothing like the Lochinvar.  For example, a comparison in total CCF usage from 2010's to 2011's bills are as follows:

Sept- 28 to 18, Oct-35 to 22, Nov- 96 to 66, Dec-168 to 102, Jan-230 to 170, and Feb-185 to 129.  During both seasons I have had the same programmable thermostats on both zones, set the same as well. 

I know it has been much milder this winter here in upstate N.Y. than years past, and I don't expect the same savings next year.  Also, those figures represent the use of a natural gas oven, dryer, and barbeque as well.  I am unsure if further dropping my setpoints will save more money or cost more in the long run due to the fin baseboards being designed to run at higher temperatures for best convection.

Again, thank for the response.        

Steve Whitbeck

MRHL

One of the problems with that boiler is when it is in space heating mode at 100% firing and switches over to indirect heating the boiler tends to overshoot the ARHL. Raise the MRHL as high as it will go (200*)  lower the ARHL to no higher than 190*, leave your heat settings at no higher than 170*. If your boiler is 150,000 BTU's or bigger than You should limit the blower speed in indirect mode to limit the output of the boiler to try to not overpower the indirect. When the boiler hits ARHL for some reason it shuts the pumps down. Post run settings don't stop this problem.

I have not gotten an answer to this problem yet from tech support.

Vinny_5

RE: MRHL

Steve, thank you for the advice.  I followed your instructions and brought the ARHL down 5* to 190* and put the SH setpoints to 170* for now with a 10* offset.  Also the hot water setpoint on the LED readout is 125*, but if I understand it correctly, it is governed only by the knob on the Amtrol water heater. It's the same water heater that was installed with the old boiler in 1998 and works excellent.  I have endless hot water, even after the wife and kids take consecutive showers and the washing machine and dishwasher have been run at the same time.  I have never noticed that the ARHL shuts down the pumps because all the lockouts I've experienced always showed both the ARHL and MRHL have tripped on the display screen. 

What do you think about bringing down the setpoints even further to say 150*-160* so it condenses even more? Can it be detrimental to the system since the baseboards are meant to run at 180*?   Other than these little glitches, this is an excellent boiler and saving lots of gas.  I just have to get it tweaked just right, but I also don't like waking up to a 60* house with only warm water to wash up with when the MRHL lockout occurs the night before and I have no idea it has occurred.  They should have a built in audible alarm similar to a smoke detector to warn the homeowner that the boiler is in lockout mode. 

Thanks for the help friend....Vinny.

Zman

Pumps

Steve,

Are you saying the main boiler circ shuts down when the boiler reaches it's target, even though there is a call for heat? I have little experience with the knight, but that is an incorrect design in any system.

Vinny,

I used to preach that baseboards must run at high temp. Articles like the one I attached as well a experimenting have taught my different.

Carl

Vinny_5

Thanks

What I did last night was initially bring the setpoint down to 170*, but after doing some more research, I decided to bring it down even further to 160* to see if there was any difference in comfort.  Well it hit 27* outside here last night but the house was just as comfortable as when I had it set to 180*.  So, I just brought it down to 150*  now as it is supposed to be mild for a bit, but getting back into the 20's later on in the week. I want to see if it has any problem keeping up with the heating demand. If it doesn't I may try 140* which should definately get it condensing more. (At least I think so).

Thanks for all the help guys and stay safe, Vinny.   

Zman

Outdoor reset

Vinny,

Are you comfortable with the outdoor reset concept? There should be 4 numbers in your mind.The coldest design outdoor temp and the associated boiler temp.You should also have the warmest outdoor temp that you intend to heat and a boiler temp associated with that day. The controller will then calculate all the days in between based on the actual outdoor temp. This way the boiler will heat the water just warm enough to match the heat loss of the building at any given outdoor temp.

Carl

Vinny_5

Outdoor reset

Carl, I am not too comfortable with the outdoor reset controls/adjustments to suit my application.  I checked my settings and they all are set to the defaults as listed on page 22 in this service manual:

 http://www.knightheatingboiler.com/knight/pdf/WB-SER.pdf

I really don't understand too much about the outdoor reset, except that it adjusts the firing rate based on the heating demand required and the outdoor temperature. Maybe you could shed some light for me.

Thanks, Vinny.

SWEI

Knob on the Amtrol water heater

Is probably an adjustable aquastat.  Does Lochinvar supply a thermistor probe with the boiler (a la Triangle Tube) or can you order one?  I suspect the boiler controls will be much happier if they know the actual temp in the IDWH.

Steve Whitbeck

Zman

What I am saying is that the boiler or indirect pump will shut down if the boiler hits either of the limits. A call for heat or hot water won't start the pumps. In ARHL the boiler just sits there untill it looses enough heat to turn back on.

Vinny_5

Hey Steve

I totally understand and agree with what you mentioned earlier about keeping the MRHL at the max setting which is where it is now and lowering the ARHL 5* so if it overshoots the setpoint enough to cause an ARHL trip, it hopefully won't go even higher (as has been in my case) and cause an MRHL trip, and just cool off a bit and restart.  That totally makes sense. I don't know why I didn't do that after my first MRHL lockout......THANKS!

What I was not 100% sure about is the offset and how it works.  The default offset is 10*, so if the setpoint is at 180*, then in theory it should max out at 190*, but it obviously went past that and overshot that temperature in my case.  I know when I set it at 170*, all was fine and the house was very comfortable with no lockouts, but I wonder what would happen if I set the offset to 1* and kept the setpoint at 180*; then it shouldn't overshoot the sepoint by much and cause a lockout?  Just running this by you. 

With the numbers I currently have it set to there is no way I am going to get a lockout now, but I will be experimenting to see how comfortable the house stays over the next week or so.  We are still supposed to have temps in the 20's here later this week, so I will be watching the modulation.

 So far since the install (6 months now) I calculated that it has saved $435.00 and 235 CCF's in natural gas, and that is with a 30,000 BTU gas garage heater that I installed right after the boiler was installed, so actual savings are even more, but I can't calculate it because I didn't have the heater installed last winter.    

Again, thanks for the input, Vinny.     

Vinny_5

SWEI

Sorry, I just noticed your reply now.  No, Lochinvar did not supply a probe with the boiler.  I just took the cover off the boiler and noticed that all there is is a red and white wire which runs down to the Amtrol unit and the knob is solely what they told me to use to adjust the hot water.  It has been absolutely perfect and provides endless hot water no matter how much  we use.  I think the tank is 41 gallons if I remember correctly and was installed in 1998, but runs like a champ.  I think the water softener helps much in our case as our water has 16 grains of hardness without it. 

Thanks, Vinny.

  

Steve Whitbeck

Offset

If you set the offset to 1* ( I don't think it will go that low ) The boiler will short cycle to death at the set point.

I would install the ODT and let the boiler outdoor reset. It will do the same job you are doing manually. Adjust it once and it will do everything after that.

Also I would see if you can install the tank sensor ( the system sensor that came with the boiler will work) inside your indirect. It will make the boiler work better. Just mount the tank sensor at the same point (height inside the tank) as the original sensor.

SWEI

DHW sensors

Again, I can't presume to speak to the Lochinvar controls here, so take this a generic advice:



An aquastat opens or closes a set of contacts at a specified temperature.  Adjusting that temperature will change the setpoint on a boiler/tank/loop/etc.  An aquastat does not provide a temperature input (other than on/off) to a control system.  In order to most efficiently manage demands for space heat and DHW, a boiler control system should have the ability to sense (and react to) the actual temperature in both systems in realtime.

Zman

Here goes

Steve, I understand what you are saying about the high limit shutting off the pumps. I have found that if the pumps don't post purge, The boiler will overheat after the heat call ends causing a lockout.These settings are I2 and I3,The default is 30 seconds.That seems about right.

Vinny, Are you adjusting E1 for domestic?

Are You adjusting B1 and B6 for the heating setpoint?I assume you have one zone hooked to sh1 and the other to sh2?



I really like this controller, it gives you tons of options.



The default reset curve in your  boiler is not likely to function well with baseboard heat. Was it changed by the original installer?



By changing the setpoint you are just squashing the upper end of the curve, you are not changing the curve.



If it were mine I would start with this:



F1 = lowest outdoor temperature seen in a typical year

F2= 65'

F3 and F8 = 160'

F4 and F9 = 100'

B1 and B2 =160'

I would leave the differential and the offset at default.

Once you set it up, If you find you are not getting the desired results at higher outdoor temps adjust F4 and F9. If your trouble is at lower outdoor temps adjust F3 and F8. The beauty of you system is you can adjust on a zone by zone basis, ie adjust F3 but not F8.

Vinny_5

Think I figured it out

Carl, no I am not using E1 for DHW, just the dial on the Amtrol and it works great.

I am using B1 and B6 to adjust the setpoints for zone 1 & 2.

I think I just found the answer to my own question and it is right there when I take the cover off the boiler written in red print which explains why I was having no issues when I had the setpoints at 170*, but got some lockouts at 180* (both with 10* offsets. It just makes sense to me now that my wall mount boiler has lower ARHL and MRHL temps than the same boiler that is a floor mount version. The defaults for SH1 and 2 were set at 180*, which is the maximum, and my installer kept it there since we have copper fin baseboards. I would routinely see the boiler initially fire up to the low 190's on very cold days without a lockout, and that would be a non issue with the floor mount models, but with the wall mount model such as mine, the MRHL is a full 10* lower than that of the floor mount model, which would explain why it would lockout the few times it did on those cold nights.  When it was set to 170* I never had a problem with a lockout or comfort either.  It just makes sense to me now, but I have to question why they lowered the ARHL and MRHL temps on the wall mount models.

Thanks, Vinny 

SWEI

E1

Is E1 a target temp for DHW?  I'll repeat my concern that the boiler does not have a temperature reading from the tank without a probe.  The aquastat generates an on/off signal (DHW call), but does not allow the boiler to see the tank temp.

Vinny_5

E1

"Is E1 a target temp for DHW? I'll repeat my concern that the boiler does not have a temperature reading from the tank without a probe. The aquastat generates an on/off signal (DHW call), but does not allow the boiler to see the tank temp."

Sorry I don't know if it's a target temperature or not.  The E1 setpoint is currently at 125* and the max is 140*.   The tank does not have a sending unit/probe attached and I don't notice a tank temperature reading on the LED screen when there is a call for DHW to fire up.  It just goes by the thermostat knob which I set at 4 1/2  and that sends the signal for the boiler to fire.  All the rest of the settings in the "E" range are at their factory defaults and like I have mentioned earlier, the hot water is just fine.

Zman

It works?

Vinny,

I sounds like you have made your system "work". That's great!

If you are looking for peak efficiency, check the settings I suggested. I  believe you have another 5-10% to go.

Carl

SWEI

DHW sensor

Just spoke with my Lochinvar rep and they do supply a thermistor, but it ships with the tank and not with the boiler.  p/n is TST2032 - you can order one and replace your aquastat, which will give those smart boiler controls a look at what is going on in that DHW tank.

Zman

E1

E1 is the boiler dhw target. E2 would be the tank temp. I would also recommend the sensor

Vinny_5

Just got my answer from Lochinvar

First of all SWEI, thanks for the info. I appreciate it.

I just needed to hear it from Lochinvar tech support myself.  I explained what I have been experiencing and how it worked fine at 170* but locked out at times when it was at 180*  and he said it has something to to with the Delta T and when a call for heat on any particular zone is satisfied, they noticed that the temperature sometimes instantly jumps up a bit, setting off the MRHL, and more so in the wall mount units like mine because of the lower hi limit as opposed to the higher hi limit in floor mount version.  He told me to adjust the setpoint to 170 or even try lower (like I have been trying) and that will definately eliminate any future lockouts.  Just that 10* difference makes all the difference.  I was concerned with efficiency and comfort, but he assured me it will make absolutely no difference in either, and I could go even lower on the setpoints if I wish. 

I still can't figure why the hi limits are lower in the wall mount versions as opposed to their floor mount cousins.

SWEI

tank sensor

*might* allow the boiler to avoid overshooting.

Vinny_5

RE: ank sensor

I may have to look into that as well.  Do you think it is an easy retrofit with a 14 year old Amtrol indirect? 

Vinny_5

Thanks Z and

Thanks to all for taking the time out to help a total stranger with your expertise guys.

It is appreciated, Vinny.

SWEI

tank sensor

Will most likely be a stainless steel capsule-shaped thing, Typically 1/4" to 3/8" diameter and an inch or two long.  Put a bit of conductive goo on it and slide into the thermowell after you remove the aquastat - assuming there is a thermowell.  If the existing aquastat does not have a thermowell, you will need to find one with the same threading as  (and about the same length as) the old aquastat.  Existing wires to the aquastat get spliced into the flying leads on the thermistor, then the boiler control needs to be told that it has a thermistor (and not a contact closure) on that input.

Steve Whitbeck

system sensor

The system sensor that came with the boiler WILL work as a tank sensor.

Yes I know that the pumps will shut down when the call for heat stops. What I didn't expect is when there is a call for heat or indirect and the boiler hits either high limit it also shuts the pumps down - NO POST PURGE of the pump. Even with the pumps set to run after a call.

SWEI

Assuming you're talking about the pipe probe Lochinvar provides

Then yes, it's the exact same part (minus the strap/clamp.)



Sounds like they need to add a post purge cycle to the shutdown logic - firmware update could easily do that, but there might be a code issue?

Mark Eatherton

The controller will automatically detect the DHW sensor...

As soon as you connect it to the low voltage board, it recognizes that it is dealing with a sensor instead of a switch (2 different inputs on the board).



The boiler, if properly programmed, will now modulate around the set point used for the production of DHW.



Regarding placing the sensor in the well of the Amtrol, some older models have a very narrow (3/8" copper) well, and you may have to grind some material off of the exterior body of the 10K sensor to get it to fit into the well. Conductive grease is a good idea. Keep it off of your hands. It doesn't wash off, it wears off...



Also remember that target temperature for DHW is different from DHW tank temperature, and is dependent upon the heat exchange effectiveness. The lower the production temperature, the better. If using a reverse indirect, your target temperature can be as little as 10 degrees F higher (150 boiler to produce 140 potable water) than your anticipated DHW tank temperature, whereas if it is a small coil, it will require as much as 40 to 50 degree F hotter (i.e. 180 boiler water for 140 tank water) water temperatures than the anticipated storage tank temperature in order to work.



Also, I find that if you give it a 20 degree offset on the DHW production side, it allows the burner to slow down before it hits the high limit like a truck hitting a brick wall. It's like a long landing strip. It lets the jet slow down before it runs off the runway...



The flexibility of this control is one of the main reasons I LOVE this boiler. No other manufacturer allows the contractor this much control access. You can program it to stand on its head and spit wooden nickels... with fire ;-)



ME

SWEI

thanks

Kept hoping someone with specific knowledge of both the Amtrol indirect and the Lochinvar controls would jump in.



Thanks, Mark.

Vinny_5

I'm confused

So what you are saying is that this wire that is currently installed on my Amtrol Boilermate's dial type thermostat will suffice in letting the Knight adjust the temperature and settings.  Currently,  it is solely adjusted by the dial itself, but if you are saying that I could have the Knight control it using the Smart System without my having to start ripping the indirect apart, it is something I would be interested in.  

I attached 2 photos to show you my setup.

Thanks, Vinny.

SWEI

that wire

Can be used for a thermistor instead of the aquastat.  You will still need to buy a 10k thermistor.

Zman

sensor

Vinny,

You need to remove the tank sensor that is attached to the back side of the adjustment knob. If memory serves me it is all under the tank (you need to remove the access panel). If you follow the wire or tube to the well,that is were the new sensor goes.

Carl

Zman

Outdoor reset

ME,

Given the depth of your Lochnivar  experience, Do you have any insight on the proper reset settings?

Carl

Vinny_5

Sorry I'm still confused

What I did is take a few pictures of the underside of the boiler and the wiring along with the Knight's board.  Maybe you could explain to me exactly what I would need to do to have the Knight take control of the indirect, if you have the time.

Sorry to be a pest, but I would be lying if I said I understood the modifications necessary based of the previous posts.  Thanks so much fellas for helping me out with this.

If it is something a DIYer like myself could tackle, I would like to take it on.

Thanks, Vinny. 

Mark Eatherton

Start low, and go up slow....

Actually, there is a scientific way of determining the highest water temperature needed. YOu do a heat loss calc for the room, taking into consideration anything that has reduced the load from the original configuration. Once the load is determined for each room, you then take an inventory of the baseboard available, and divide the calculated load by the linear feet of baseboard. Then, using Slantfins baseboard output chart, which goes clear down to 140 degrees F, determine what the worst case scenario will be, and use that as the HI ODR setting, when the OSA is at design conditions.



Once you've determined what THAT set point is, I'd still experiment and knock 5 degrees F off the calculated temperature and see how the house in real time works under those conditions. I'd keep doing that until I hit a point where comfort is fading, then bump it back up 5 degrees F.



Remember, even in situations where I know for a FACT that things were sized properly, when I show up at design condition, and the house is staying comfortable, but the boiler is doing a 50% duty cycle, it tells me that the system is 2 times bigger than it needs to be.



The lower you can go, the better the modcon will perform.



Luck be with ye...



ME

Zman

sensor

Vinny,

The tube with the label goes into a "well" in the bottom of you tank. It has a bulb on the end of it and it is removable. The new sensor will go inside the well in place of the old one. You may have to remove a nut or a clip to get it out. I can't tell from you picture.

Carl

Vinny_5

Ok

Now I got it.....Thanks.   From what I see on the label I dont have to drain the indirect to replace the sensor either, or am I mistaken?

Thanks you all once again for putting up with my ignorance.

Vinny. 

SWEI

the label

On that capillary tube says you have a thermowell.  Pull the capillary tube out of the thermowell and insert the new probe.

Jean-David Beyer

Slantfins baseboard output chart,

Some of those charts now go down to 110F. My BaseLine 2000, for example. And since I have that oversized, I actually run 110F water in them until the outdoor temperature goes below 50F, when the supply water slowly goes up to 135F when it is 6F outside. Design temperature around here is 14F. I did that specifically so I could condense all the time.