Lochinvar Knight MRHL Lockout
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.
Your water temperature should be set to run as low as possible yet maintain a temperature in your home. My opinion is that you should not set back the heat in your home at night as it will take many hours to recover if the boiler is dialed in correctly. By maintaining a lower water temperature for longer periods of time, you generally will save more money maintaining a lower water temp and n setting your stat back. Your boiler should use an outdoor sensor. I am assumed it is hooked up? This will allow the boiler to automatically lower the water temperature as the temperature increases outside. I am not sure where you live nor what your baseboard is designed for temperature wise. If it really is designed for 180° then it may be more beneficial to add more baseboard to the home, or perhaps put some radiant tubing in which will allow you to lower the water temperature even more, the numbers y describe for setup are in my opinion not correct. Again I have not seen your installation. It may be beneficial to have someone else familure with the boiler look at it, or request that a factory rep visit your home.
We have a number of baseboard radiator systems that will run at 130-140F in mild temps. Unlike cast iron which will give heat even at 90F, copper fin convectors (Slantfin perhaps) don't have published outputs below 160F typically but that doesn't mean it wont provide some heat. The 180F is for design conditions which could be 0 or -5F perhaps, depending where you are located.
You need to experiment with the "slope" to determine the lowest temp that the system can be run. Just don't expect too much below 130-140F.
You may have cast iron baseboards which will heat with lower temps.
Thanks for the input guys. I am about 70 miles NW of NYC. I should have mentioned that it does have an outdoor reset and modulates quite often. I often notice it running at 20%, especially when it is a bit warmer out. The house is more comfortable as well without the old heat/stop/heat/stop type of system I had. I do have copper fin baseboards and the old cast iron boiler ran them at 180*. Radiant is not a possible option as I am on a concrete slab with no underfloor access.
I had a Beckett Heat Manager installed on my old cast iron boiler about 6 years ago, which helped my gas usage drop a bit, but nothing in comparison to the Lochinvar. The old boiler was listed at 81% effiency but was tested and proved to be operating at 79%. For example, since installing the Locinvar, 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, so I know it it modulating and saving gas. Seems the colder it gets, the more gas I am saving compared to the same period last year.
I just want to get it tweaked just right where there is the proper comfort level but with the lowest possible gas usage, along without any further lockouts.
Again, thank you both for the quick assistance and advice, Vinny.
I'll ask a loaded question. How efficient is your new boiler?
Well, the tag says 96%, but I believe that would be with radiant heat, so I believe I am getting a bit less. I do know that I have saved much gas during the last few months as compared to the same period last year. What I also forgot to mention is I also installed a gas garage heater in November as well, but I don't use it everyday. Even with that, the gas savings have been impressive, although it has been very mild for my area this winter.
I do not know the exact numbers, but I would expect your unit to be top efficiency when a return water of around 120° is achieved. When the boiler is running near other limit you,have it set for I would expect high 80% efficiency at best.
The situation you are describing with your fault is not all that uncommon. As I said before I think the settings can be adjusted to a lower water temperature and your problems will go away. Good luck
Thank you. I will be experimenting this next month with lowering the setpoints even more, maybe down to as low as 140*, but it sort of does that automatically with the outdoor reset. All the times the MRHL lockouts occurred were during sub-freezing outdoor temperatures.
I appreciate you taking the time to help me out on this matter.
Take care, Vinny.
I just figured out how to load a few pics of the unit:
I'll be the bad guy.
The install looks diy, but that's none of my business and I don't care, you came here for advice.
You can tinker with the controls all you want to, they will not fix the real problem.
The real problem is there is absolutely nothing correct about the system and how it's piped.
This is not a site for diy advice, maybe someone over at HH will post what needs to be done.
If you had called me out to fix this, I'd cut the supply and return tubes where they come out of the bottom of the cabinet, tear the rest off the wall and do it over, properly. This is Hydronics 101 and all the tweaking in the world is only going to cover up the real problem. The system you have will never allow the boiler to perform as it was designed, and all the tweaks will only be a band-aid.
The piping to the right side of the boiler makes it a very busy area indeed and I'm not sure what the piping is to the left of the boiler as it's not shown.
The problem you seem to be experiencing is due to either a lack of water flow at times or the boiler firing at too high a rate at times. The ARHL error is for the automatic reset high limit, which trips at 200°F and resets when the boiler temperature drops to 190°F. If however the boiler temperature continues to climb from 200° up to 210°F then it goes into a MRHL, manual reset high limit. This is where the 'lockout' comes into play. I see that you have 2 zones of heat as well as a separate loop for the domestic indirect water heater. I cannot see what pumps are installed but Knight boilers MUST have proper pumps or you'll have devilish problems. Your installer has spoken with tech support you stated so I must therefore assume you have adequate pump capacity under all conditions but it will take some detective work to find the ultimate cause. It could even be a sensor or wiring issue but only someone on scene can discover that.
As far as heating is concerned, I've found about 1 out of 12 or 15 homes that actually have had a baseboard system installed using a proper load analysis. Most are over served so running 170° or even 160° heating water isn't likely to be a show stopper, even in cold weather. And you'll get useful heat at even lower water temperatures. Just FYI, the 180° design temperature to which you refer is needed only at outdoor design temperature. At all other higher temperatures you can get by with lower temperatures.
If YOU want change, YOU have to first change.
If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!
The boiler room is very small and the old boiler's plumbing was very messy and all over the place. I asked them to locate this one on the very narrow back wall instead of the side where the old one was, and they also re-located the indirect to the left of the boiler (that is some of the vertical piping you see).
The system pump is what came with the Lochinvar and they said they must use that with it. Unfortunately the manual had a typo and it was confirmed by Lochinvar. The ARHL maximum setting is 195* and the MRHL is 200*, and like I had mentioned before, it only has locked out on the coldest of nights, when I had the setpoints to 180*. Once I brought them down just 10* I had no problems with the unit at all. I just recently moved them back to 180* last week, and that's when I had the lockout again recently.
So far since the install (6 months now) I calculated that it has saved $435.00 and 235 CCF in gas, and that is with my running a 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.
Thanks for the help, Vinny.
Boiler Outlet and inlet is backwards.
On top of that, let me guess, system pressure is set at 10psi?
Last edited by hvacvegas; 03-07-2012 at 11:17 PM.
"Better tell the sandman to stay away, because we're gonna be workin on this one all night."
"Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."
"Just get it done son."