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>.5" W.C pressure drop on ignition (HTP-EL150, related discussion links included)

np_mdbr
np_mdbr Member Posts: 82
in THE MAIN WALL

I didn't want to add on to a thread that's now over 3 months old, so this is really a follow on to a discussion that I started back in July '24 after I experienced the "gunshot" sound out of my HTP-EL150 boiler due to delayed ignition.

See this thread for the details on this discussion. I had a tech come out who tore the unit apart and we discovered that the gasket that connects the boiler unit to the flue was completely disintegrated which was allowing extra air into the combustion chamber. At that time, it seemed like this was the best explanation for the delayed ignition. Additionally, the flue gas sensor had been corroded by flue gases which was causing an acidic leak onto the field circuit board, which I cleaned and re-soldered (pics available upon request :).

HTP does not sell this flue gasket. You either have to make your own or spend $15k on a new unit. I opted to build my own.

I ordered some sheets of PTFE, cut out a new gasket, applied some hi-temp silicone (meant for chimneys and flues) to the connection and reinstalled the boiler-to-flue piece of black ABS.

I also invested in a Klein manometer and a Testo 310 combustion analyzer.

Today, after connecting the manometer to measure ignition pressure drop on the gas inlet as suggested by @daveradar in the post referenced above, I fired the unit. I tried three times. Each time, the unit failed to fire and started doing the delayed ignition thing again (read small explosion). I could smell burned and fresh LP after each attempt, and in one instance, I let the unit try as many times as it could before entering a fault state (F09 - no flame on ignition).

Here's the video that leads to the F09 fault (I was leaving the room just in case of a large explosion).

The manometer indicated a -2.5" pressure drop in these cases as you can see in this subsequent video.

This is far beyond the drop that @daveradar suggests, and he suggests checking the gas regulator first followed by the unit's gas valve.

I'll be contacting our LP supplier on Monday to have them check the regulator. I am looking for suggestions on what to have them look for and what I might be able to check myself in the meantime.

Appreciate all of the help. This forum has kept me sane as I deal with no hot water for going on 3 months now :).

Comments

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,212

    With that much of a pressure drop, you either need a new regulator or the piping to the boiler is undersized.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    np_mdbrGGross
  • np_mdbr
    np_mdbr Member Posts: 82

    Went in and tried again this morning. I am pretty sure I had not allowed my manometer to stabilize properly before taking the measurements yesterday. Below, I outline the process I followed, with images of the manometer readings.

    Would appreciate any insight into this process, which appears to show that the pressure drop is not as bad as expected (~.26").

    And today I noticed that even when I hear the the spark attempt to ignite the gas mixture, there is no ignition any more, just spark that lasts for a couple of seconds. Is this expected after the gas line has been shut off overnight, for example?

    Process:

    1. Gas line has been shut off for a number of hours (no pressure to the gas valve).
    2. Power up manometer with no lines connected. Zero out manometer.
    3. Connect line from inlet valve to manometer P1.
    4. Observe a very slight increase in pressure from 0.00" to 0.20".
    5. Open gas line. Observe a pressure increase to 12.90". Wait 5 minutes to allow the pressure to settle to ~12.70".
    6. Enter Max/Min/Avg mode on manometer.
    7. Create heat demand, causing the unit to attempt to fire.
    8. Observe spark sound but no ignition.
    9. Cut power to the boiler after the first failed ignition.
    10. Observe manometer readings: MAX=12.91", MIN=12.44", AVG=12.87".

    So, the pressure drop here is actually only .26" which is well within the @daveradar suggestion of no more than .5".

    Could the gas valve itself be the culprit at this point? What else should I be checking?

    Interestingly, the manual strongly advises against measuring or adjusting anything on the outlet side of the gas valve, so I have not touched that side. Can anything be learned by connecting the manometer to the outlet side (against the advice of the manufacturer)?

    From the manual: "DO NOT adjust or attempt to measure gas valve outlet pressure. The gas valve is factory-set for the correct outlet pressure and requires no field adjustment. Attempts by the installer to adjust or measure the gas valve outlet pressure could result in damage to the valve and cause substantial property damage, severe personal injury, or death."

    Images:

    (1 of 4) - Reading after letting the manometer "settle" after opening the gas valve:

    image.png

    (2 of 4) - MAX reading after letting the unit attempt to fire once:

    image.png

    (3 of 4) - MIN reading after letting the unit attempt to fire once:

    image.png

    (4 of 4) - AVG reading after letting the unit attempt to fire once:

    image.png

  • np_mdbr
    np_mdbr Member Posts: 82

    One Hour Later…

    I waited an hour and then ran through the same process that I outlined above.

    This time, the first spark lit the mixture resulting in delayed ignition with a pressure drop all the way down to 10.91". See pics below.

    (1 of 4) - Reading after letting the manometer "settle" after opening the gas valve:

    image.png

    (2 of 4) - MAX reading after letting the unit attempt to fire once:

    image.png

    (3 of 4) - MIN reading after letting the unit attempt to fire once:

    image.png

    (4 of 4) - AVG reading after letting the unit attempt to fire once:

    image.png

  • np_mdbr
    np_mdbr Member Posts: 82
    edited October 27

    I gathered more data in the form a spreadsheet. Out of five total attempts to fire the boiler thus far, two have failed to produce an ignition event. These two failed events clearly correlate with a pressure drop that is within spec (<.5" W.C.).

    The others, where ignition is achieved (but not sustained), clearly correlate with a pressure drop that is well outside spec. I assume this continues to point to a bad regulator (I have a two-stage system - one regulator at the propane tank and one at the house exterior).

    Thoughts, comments are welcome…

    image.png

  • mattmia2
    mattmia2 Member Posts: 10,826

    sounds like the needle in the house regulator is sticking in the seat. you can measure it near the regulator on both sides to confirm it is the regulator and not the size of the piping or the upstream regulator.

  • np_mdbr
    np_mdbr Member Posts: 82
    edited October 28

    Thanks for the guidance @mattmia2 ! Since the sizing of the pipe has not changed since initial installation (over 20 years ago now), I am going to go with a regulator issue.

    We did have a period last winter where temperatures dropped below -40F for over 4 or 5 days. I am now wondering if that period was enough to damage the regulator(s) enough that they started to fail. We did not notice this firing issue after that deep-freeze.

    Hmm…

  • mattmia2
    mattmia2 Member Posts: 10,826

    The -40 could cause the vent on the regulator to ice or the propane to have trouble evaporating fast enough but isn't likely to cause permanent damage.

  • np_mdbr
    np_mdbr Member Posts: 82

    Had the LP tech come by this morning and look at the primary and secondary valves. He said they hadn't been adjusted since their installation, which was back in the late 90's. He suggested I have them replaced, which I have scheduled. Here's an image of his report:

    image.png

    After he had finished his work, I checked static pressure at the gas inlet, which read 14.11" after settling. This value is too high according to the manual. So I went out and adjusted the secondary valve down to 13.25".

    I then tried firing the unit. The first three attempts failed. Static pressure was at 13.19". During firing, pressure dropped all the way to 11.26", still way out of spec.

    The fourth attempt was a rather spectacular and deafening explosion that blew apart the condensate unit.

    I have video of this event, but here are some pics of the aftermath. I will be starting a new thread based on this unsettling event.

    Condensate tank completely disintegrated:

    image.png

    Shards of condensate tank blown across the space:

    image.png

  • mattmia2
    mattmia2 Member Posts: 10,826

    did all that crud come out of the boiler? When was the last time it was cleaned?

  • np_mdbr
    np_mdbr Member Posts: 82

    @mattmia2 That crud is from the bottom of the condensate tank. The boiler housing was cleaned recently, and the boiler tech that came out a month ago to take a look agreed that the boiler housing was looking good.

  • SuperTech
    SuperTech Member Posts: 2,405
    https://forum.heatinghelp.com/discussion/comment/1816751#Comment_1816751

    Obviously he didn't clean the condensate trap. It shouldn't have been dry if he just serviced it. Cleaning the boiler requires water to flush all that crap out. Like I said in the other thread, a condensing boiler from the 90's is past it's expiration date and it seems like it has had a rough life full of neglect. I'm not sure if it's a worthwhile pursuit to continue to keep operating it.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,381

    The other possibility is moisture in the propane. Propane is stored as a liquid and as it changes to a gas is acts like a refrigerant if there is moisture in the propane it can freeze at a regulator. Or you have a bad regulator

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