Htp UFT 80 pulsing during high fire

doeber21

Hello everyone, 

I'm looking for some help to diagnose a problem my Htp Uft has recently revealed. It is still summer here in Minnesota so hopefully I have some to to figure this out.

I installed the boiler last fall for an existing radiant floor system in the basement of my house. I replaced a Weil-Mclain cgi gold that was grossly over sized. (I got tired of hearing fire on and off) After doing many hours of load calcs I settled on the UFT 80. I added a 2 pipe system 40 gal water heater for a buffer tank to help with my 2 micro zones (master bath and basement shop area).

It ran great all winter. I recently fired it up to stretch its legs and it was making this pulsing noise when reaching high fire. Almost sounded like helicopter blade hitting the air. So first things first, I jumped on the wall and did some searching. I ran across a post about the broken flap inside the intake. So I pulled the fan out and nope, not that. Then I read about the clogged heat exchangers and bingo. The tops of each tube was caked. So I got out the shop vac and screwdriver and cleaned them all up. Ran the hacksaw blade down each one and it slipped right to the bottom. Removed the condensate trap, cleaned that out. Shined a flash light up the exchanger and it was clean. Put it all back together and nope, that wasn't it.

So finally my questions.

1. What would cause the noise of the pulsing in the heat exchanger?

2. Why would the combustion chamber fire tubes be clogged up on the top side.

Thanks for any help or comments.

I added a picture of the top of the heat exchanger before I cleaned it. And yes a combustion analysis was completed when installed.

I do have a video of the unit pulsing while running, what's the best way to upload that? It's telling me the format is incorrect.

Thanks!

Jamie Hall

Check both intake and exhaust ducts for any kind of obstruction.

HomerJSmith

Re-do a combustion analysis with a recently calibrated meter. NG or LP?

doeber21

Jamie Hall said:

Check both intake and exhaust ducts for any kind of obstruction.

I will check for any clogged exhaust and intake tonight.

HomerJSmith said:

Re-do a combustion analysis with a recently calibrated meter. NG or LP?

It is natural gas.
Combustion analyzer will be here tomorrow.

Thanks for the advice I will update on my findings.

GroundUp

Have you tried locking out high fire? I had a problem child UFT-80 that was making that huffing sound among several other issues- but setting it to 80% maximum fire solved the problem. Maybe you need the whole 80k input so that wouldn't be a permanent solution, but it may point you in the right direction. In hindsight I believe it may have been (in my case) an issue with the gas regulator being too close to the boiler, but I'm not going to tear it apart any further until it starts acting up again.

doeber21

I have not tried to lock out the high fire. I will give that a try if the combustion is where it should be. I do not need the 80K, probably only about half that until the system is up to temp and then maybe 20%. Is there any issue with the boiler never running at high fire and just keeping it limited?

GGross

@doeber21
In my experience most mod-con boilers run just fine never seeing high-fire. You will find differing opinions on this with evidence to support both sides. In my opinion it is not a problem for a boiler like that.

EBEBRATT-Ed

@doeber21. I would check incoming gas pressure to make sure the pressure is correct and steady. Also burner manifold pressure.

Is the gas line black pipe or flexible CSST?

109A_5

Hello @doeber21, you may want check this post, similar noise, different boiler.

https://forum.heatinghelp.com/discussion/188890/lochinvar-parts-conundrum

It was an older system and hopefully yours does not have the age related dilapidation that was found in that system. However he found another place where the debris liked to collect.

doeber21 said:

The tops of each tube was caked.
2. Why would the combustion chamber fire tubes be clogged up on the top side.

Ever change an air filter on a car ? Where does all that dirt and stuff come from ? When your boiler is running it is pulling in unfiltered outside air and then burning whatever junk and debris is in the intake air (and any impurities in the gas). The top of the heat exchanger is probably the first place where that burnt vaporized junk can collect and it may stick to similar debris compounding the matter. As the exhaust gasses cool moving through the system other stuff may precipitate out and collect elsewhere.

They put cabin air filters in cars maybe boiler air filters are next.

Ironman

I’m not sure that using a hack saw blade was a good idea as it could damage the turbulator fins.

If the boiler hasn’t run all summer, you may have some air in the gas line that needs to be purged through the burner on a lower fire.

mattmia2

109A_5 said:

Ever change an air filter on a car ? Where does all that dirt and stuff come from ? When your boiler is running it is pulling in unfiltered outside air and then burning whatever junk and debris is in the intake air (and any impurities in the gas). The top of the heat exchanger is probably the first place where that burnt vaporized junk can collect and it may stick to similar debris compounding the matter. As the exhaust gasses cool moving through the system other stuff may precipitate out and collect elsewhere.

Especially if you have cottonwood or something like that.

doeber21

Heres an update:

No obstructions in intake or exhaust.

Combustion analyzer came back at the low fire within the tolerances but high fire kept jumping above the 10% CO2. I tried adjusting the low fire both up and down for CO2 levels and each time the high fire kept jumping up. Checking fuel pressure showed that their may be a fuel delivery issue as it is dropping 2" on high fire. It is currently 6' of CSST to the boiler from the gas tree. I will pipe with black and check the results. Do you think this could be it? Could it be the gas pressure regulator or just the CSST? Would this drop in pressure cause the CO2 to go out of limits on high fire?

Thanks

@Ironman, the hacksaw blade was an old dull one and just used to see if there was any other obstructions.

mattmia2

Where are you measuring the pressure? What is the pressure dropping to? You may have a bad service regulator or something weird like water in the gas lines.

HomerJSmith

6' of CSST

6' you say. Well, CSST need to be sized based upon the boiler needs. The tag on the CSST gives you the delivery to the boiler. I would want CSST to be as short and as large as necessary.

The boiler probably draws a vacuum on the line. The distance from the meter to the boiler and other appliance take-offs is an important consideration for the gas delivery to the boiler. Have you added any other gas burning appliances?

I don't think HTP recommends CSST as a connection.

pedmec

where are you measuring gas pressure? you should be reading in inches of water column not psi. if your getting an increase in co2 your not starving of gas. your starving of oxygen. what are your excess o2 #

doeber21

@mattmia2
I was measuring the gas inlet side of the gas valve on the boiler. When the boiler is off it is reading 11"WC on low fire it is 10.42 and high fire it is 9.

@HomerJSmith
I know that is not ideal. One of those things where I had the gas line on hand and wanted to see the thing fire. Always planned on repiping it but never did because it worked great all last year and all the numbers checked out. So I thought I would just run it. This is piped off the same valve on the gas tree that the previous 100Kbtu boiler ran from (that was about 4' of 1/2" black pipe to that boiler. The only other things on this side of the regulator are a gas fire place (rarely used except shoulder season) and a gas range that is in the basement for canning (only gets used before heating season). This is all fed with 2 psi gas maybe 40' from outside meter. There is another branch of the 2 psi gas that runs to a furnace room located in the middle of the house that has another regulator feeding the furnace and another fireplace upstairs.

@pedmec
I will need to test again and confirm the o2 number, seems I didn't jot that down. What am I looking for? If it goes up or down? What would this indicate not enough intake air?

Thanks again for the help

pedmec

your CO2 should go down with and increase in oxygen. when set up properly. you should be looking at CO # too. improper mixing of the gas and oxygen will result in high CO and safety is more important than efficiency. its all related. you should have about 25-30% excess O2 thou you can be outside these #

109A_5

Just my opinion, until you repair pulsing noise situation you may never get 'normal combustion numbers' on high fire. You may be able to lock out 100% high fire but that is just a band aid solution and the problem may come back at a lower % of fire as time goes on if left un-repaired.

I would find out what changed between the former normal operation and now. Apparently something changed.

doeber21

@pedmec
The CO numbers were good, well below the limits of 175ppm on low fire and high fire. Low fire was about 75ppm and high fire was about 100ppm.
I will check to see what the o2 numbers are doing during low and high fire.

@109A_5
I agree. I thought I had figured it out with the blocked heat exchanger. I suppose that is why I asked the question on here, to see if anyone had more suggestions on what I should be looking for. I also agree that lower the high fire would just be a band-aid. I would like to figure out where things changed.

109A_5

Hello @doeber21,

Were you able to inspect the bottom of the heat exchanger where it transitions to the flue duct for any debris or compromised seals, gaskets, cracks or other leaks?

Condensate hose plugged external to the boiler ?

doeber21

@109A_5 ,

I was able to take a look at all of that. It all looked great.
I ran the hose into a bucket while operating the boiler and the condensate hose was flowing just fine.

doeber21

Update:

HTP is sending me a new Combustion blower. After doing my last combustion test I got an Error Code 61.
I called tech support and filled them in on what was happening. They had me troubleshoot the error code. It was determined that I needed a new blower. I will install when that arrives and see if that is it.

On another note:

While running another combustion test to see where my excess o2 was at I let the boiler run on low and heat the whole loop up. Thought if there was air in the gas or something like that I could work that out of the system. I than slowly ramped it up to 100% fire. Doing this made the noise a lot less noticeable. The Co2 levels had also leveled out. Could this just be a condition that is present while the system warms up.
I'm getting a 19 degree delta across the boiler, so I believe the flow is good.

doeber21

Welp, the blower just got delivered. Packing slip says for a UFT 199. Has a different intake/ venturi on it... My boiler is a 80K. Hmm

109A_5

Hello @doeber21,

Looks like the fan 'only' is the same part number between the 80 and the 199. The mixer is different. Maybe that is all they had and you have to swap the mixing assembly.

Some interesting things here if you have not seen this post yet.
https://forum.heatinghelp.com/discussion/160404/htp-uft80-foghorn-noise
Do you have the minimum equivalent length ? 14' in the manual I am looking at.
https://htproducts.com/literature/lp-542.pdf

mattmia2

I used regular 90s to get the minimum developed length.

pedmec

i would definitely get the correct mixer. it can definitely affect your combustion operation. for some reason htp seems to have combustion issues. earlier versions on some of their boilers required modifications. one fix they had was an adapter on the air intake opening. a 3 x 2 reducer with a 3' hose to reduce the rumbling.
on weil mclain ultra boilers they have what they call a silencer. installed basically in the same location. intake connected direct to motor. when it cracks and falls off, the boiler will rumble also.

doeber21

I swapped the mixing assembly and installed the new fan. It does seem quieter as far as pulsing goes, that has seemed to clear up. But now there seems to be a rattle inside the heat exchanger. This only happens during combustion. The higher the burn rate the worse the rattle. This does not happen when it is only the circulator running. It is odd because if the boiler is off and I bump the heat exchanger there seems like something rattling inside the heat exchanger. I will give HTP tech a call today. Just wondering if anyone else had a rattle in their exchanger if you give it a shake.

GGross

@doeber21
Is it possible that something was left a little loose when you replaced the fan and you may be mistaking a rattling from the heat exchanger with a rattling from a loose screw on the fan? This would make sense why it only rattles during combustion, and ramps up and down with the fire rate, and not when the circulator is running.

mattmia2

Are you sure it didn't do this before? M uft-100 has always done a little bit of cavitation or something like that in the hx under certain conditions.

doeber21

Here is what it sounds like. It does this from about 40% to 100% firing rate.  I checked for anything loose and did not find anything. The sound is not there when just the fan runs or just the circulator running. 

https://youtube.com/shorts/kk06zITZNeY?feature=share

HomerJSmith

Try to isolate the sound with a mechanic's stethoscope. You can get one at Harbor Freight or any auto parts store. They're cheap.

109A_5

doeber21 said:

It is odd because if the boiler is off and I bump the heat exchanger there seems like something rattling inside the heat exchanger.

Yes seems odd, maybe there is still some debris in there.

doeber21

Yes, very odd. I used the ol screwdriver to the ear trick and can't seem to isolate it to a specific area. I can just hear it throughout the heat exchanger.