Lochinvar Knight Fire Tube Cleaning Suggestions?

BigRob

Ok, so our WHN199 has been on the wall 10 years and I noticed the flue temperature is not below the incoming water temps as much as it used to be. Because of that and the 10 years, I think it's time to take the burner off and clean it up. I'm also going to stick my bore scope up the water side and see what's going on there.

My plan is:

To spray CLR on the combustion side and let it sit, then scotch bright it, then use a long skinny brush to hit the fire tubes. Condensate still drips a good amount so I'm curious to see what's up. Maybe I will plug the bottom and fill it up with CLR. Not sure of a good way to plug it.

For the water side, if I need to, I gave a 5 gallon bucket and submersible pump to circulate CLR or whatever through the isolated HX. Any tips here? The system was passivated with Rohmar and has been running their protector for years, too.

I'll post pictures from the combustion and water side, including the borescope pics.

Any tips and tricks?

JUGHNE

I had a lot of problems with a water tube Loch.
It would lock out on high limit numerous times.
The system pump was drawing less amps than original install.
The pump must have been just marginal in size to begin with.
Stepped up a pump size and have not been call back.

Cleaning is still a good idea.

Looking forward to your pictures.

Derheatmeister

On these type of HX we plug the bottom with a expandable type plug (Hardwear store), fill it with a CLR mixture and let it soak..Just make sure that the expanding plug is secure and put a bucket under the HX..
You can also rig up a hose with a valve so that you can control the draining of the CLR better.
We do not stick anything down the fire tubes since it may get stuck on the flat areas.

We made a high pressure cleaning machine for the Viessmann,Baxi,Munchkin type of Heatexchangers...It looks something like the Sotin **** 1: https://www.google.com/imgres?imgurl=https://m.media-amazon.com/images/I/31IyEQYjtOL._AC_.jpg&imgrefurl=https://www.amazon.co.uk/Combustion-Chamber-Kit-Sotimentsd-WTF1/dp/B007GJYED2&tbnid=Nmsajw1ajKysEM&vet=12ahUKEwiOzsGg89H1AhURkmoFHeAnCTwQMygAegQIARAw..i&docid=_U2WPEy_ML0WcM&w=266&h=268&itg=1&q=Sotin WTF 1&ved=2ahUKEwiOzsGg89H1AhURkmoFHeAnCTwQMygAegQIARAw

https://www.sotin.de

As for the water side...Rhomar makes a good product and you should follow up with them on the chemistry (Send a sample to them).

BigRob

Thanks for the input, guys. Do you recall if the expandable plug a 1 incher?

BigRob

Also, I've been using the boiler pump speed control for a number of years. It's a bigger pump so at low fire the min gpm is 8, which is around 10F deltaT or below at low fire. The pump is an Armstrong compass H 20-20 because it has the 0-10V input. I have had a couple random high limits I've been trying to track down. I was leaning towards power quality knocking out the compass. We have pretty dirty power in SF and lots of surges/browns. My surge protector light is out, so need to change that outlet, too. Anyway, the random high limits got me focused on maintenance. The lockouts seem to happen on cold days when the boiler is high firing. Figured the pump got knocked out by a brown/surge and high limited. I will post back pics.

hot_rod

Is it piped primary secondary or with a hydraulic separator? If so the boiler pump is just circulating that loop.

The manual should show min. flow rates. I would suspect a dirty HX before a bad circulator causing the high limit.

If it is direct piped with zones, it could be lack of flow under certain conditions causing lock outs?

The control may keep track of those lock outs and conditions that caused it.

The pump is powered from the boiler so a power condition should knock out everything. If the boiler is running high temperature and power goes out, it could creep up a bit and trip limit.

I think both operating limit and high temperature limit are adjustable. I set my high limit at 180, and 210°.

JUGHNE

199,000 BTUH sounds high for San Francisco, what is this heating ?

BigRob

Hey Rod, JUG: It's a SEP4 with Armstrong compass H for the boiler loop; Taco VR ECM for the thin slabs in twelve ~900sf condos. Then an Alpha for 5 panel radiators. Alpha pumps through zoned manifold. The thin slabs use Caleffi zone valves and a 4 way motorized mixing valve. The 199k works very well heating this mid rise condo building, but its usually 55F/65F here. Some weeks are in the 40s. This year has been colder, so more days in the high 40s and low 50s.

Maybe you are right about the pump. Lochinvar specs a 26-99 for the 199 and it's 30gpm at 2ft vs the compass 18gpm at 2ft. The issue did start when I installed the Compass not this season but last. It only happened a couple times, stopped, now back. Seemed like the compass would not be an issue because on high power speed the boiler delta T is very low even with the compass most of the time; could be an issue at 100% fire. Need to check it. The high limit was initially set to 200F. I lowered it down to 160F, just the other day. The thing is, the set point is 120F and I allow it to creep to 140F for the rads while the mixer protects the slabs. For the 200F lockout to trip I would expect the pump to stop suddenly- doesn't seem like a creep problem. I did some testing that seemed to confirm this. Maybe there are some chunks floating about that are creating a blockage. I changed the high limit reset to auto reset while I was out of town. Just now I'm wondering if the high limit will log when set to auto reset. I need to test that. There haven't been any issues as of late, but it also hasn't been cold recently and it seems to happen at high fire.

I was thinking the Armstrong was getting hit with a spike or brown out, which shut it down (it has an error for both), then it would reset when power cycled by the boiler relay after the pump timeout. The boiler relay just passes house 120V so it will not filter a power event like the 120V/24V transformer that powers the boiler electronics. Armstrong email tech support was useless. All I wanted to know after 3 back and forths is if the pump stops when a power quality error occurs. The guy seemed to be actively avoiding a direct answer. Maybe it was a language barrier.

I was also thinking the Compass inrush might be making the relay charred. Then I noticed the flue temperature. There are no leaks in the system. I don't even have makeup connected to the city water because I got tired of dealing with the yearly backflow test. It's been at constant pressure for years. Before that it was in bad shape and I spent a lot of time unplugging pex- so much iron oxide. Once I got it clean I passivated (not sure it does much in an old system) and added the protek. So, I'm very curious about what's going on in the water side of the HX.

One thing I did notice one cold night- the Taco VR was pumping 15gpm and the system pressure was being pulled lower which I thought was odd. I slowed the pump down and the pressure was back to normal. It kinda confused me. I thought the pressure always stays constant when pumping away from the expansion tank. The expansion tank is connected close to the Compass inlet. Seems fine. The Taco is set to 20ft. I played with the settings and set the head to the knee of the power curve. It made me wonder if the SEP4 baffles are clogged, so I will check that when I clean the HX and change out all the crappy pressure gauges. Maybe when the VR is going full out it starved the Compass. I was using a 26-99 before the compass and I think the compass was on medium for a while. That might have been an error.

hot_rod

The pump on my Loch Knight 50 is a Grundfos OEM model, maybe it has a unique algorithm to work with the control?  I’m not sure another 0-10 pump could be subst?

BigRob

I think the boiler deltaT control is a normal PID type, but I did notice the 0-10V output signal was not what I expected with the compass in the loop. With the Compass connected and 100% commanded from the boiler, max output is ~7V. Probably need to add some resistance to the circuit or the output got screwed up somehow. Before the compass I was using a UP26-99 with a triac 0-10V speed control. Worked fine. Should have left it alone, but have been fascinated and in hobby mode regarding ECMs. So, yes, scaling can be an issue. As it is now, anything over 60% commanded is taken by the compass as 100%. I bought a scaling box but haven't added it yet. Also, min voltage from the knight is 2.5V. The compass minimum is 2V and anything under 2V turns off the pump, which was my first suspect when this started happening last season. I have not been able to reproduce that failure mode, though. At 2.5V, the compass is flowing 8gpm and the HX deltaT is <10F at 20% firing. If the Knight could command 2V, the compass could probably maintain 20F DeltaT throughout most of the firing range. I don't understand the 20F HX deltaT though. Does the gradient across the HX aid heat transfer?

I need to setup a video camera to catch this pump issue, most likely. Or the HX and burner are super dirty. We shall see!

hot_rod

Is the VS circulator intended to maintain a certain delta, or maintain minimum flow. The manual seems to indicate it prevents too low of flow rates?
Seems mine is always around a 5° regardless of the fi4ing rate.

BigRob

DeltaT is controlled by pump speed, so if your pump is too big you would never get to 20F.

hot_rod

BigRob said:

DeltaT is controlled by pump speed, so if your pump is too big you would never get to 20F.

Mine shipped with the Grundfos, it has an OEM model number

BigRob

I think the OEM pump is the Alpha1 26-99. Not 100% sure though.

https://product-selection.grundfos.com/us/products/alpha-north-america/alpha1-26-99-north-america?tab=models