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Steam Flashing in Navien tankless

DavidSa
DavidSa Member Posts: 12
I I have a problem with steam flashing (maybe) in my Navien CR240A tankless heater but I just can’t figure it out. 

When heating water it makes loud popping and crackling and clanging sounds. Hard to pinpoint the sound exactly but it seems to be in the HE. I will try to attach a video. 
No sounds if I leave the heater off and just open the relief valve.  I think that would flow though the heater so if the issue is mechanical it should also happen?

I did a flush with hot vinegar 2 years ago and I think I got it really clean. That was only the 2nd flush in its 15 yr life. Since the sounds started, I did a 3rd vinegar flush last week. The resulting flush water unsurprisingly looked quite clean. 

I check the inlet filter: clean. 
I checked the air intake: cleaned out a bit of fuzz but not bad. 
I disassembled 80% of the connections in the piping and reassembled ( 2 orings were leaking was the main motivation for that). Everything looked good although I didn’t think to look down each pipe to look for obstructions. 
I checked the flow sensor: it looked ok but I had a spare so I changed it. 
The temp is set to 120F as always. 
There are no error codes that I can see but I don’t know how to specifically check. 

I haven’t done the following:
Measure any pressures upstream or downstream of the unit. I can’t really figure out how to. Many years ago I measured the city supply pressure at 125psi. I doubt it changed. 
Assess the inlet valve for obstructions or function. I’m thinking of opening that up next. 
Measure temperature, although it doesn’t seem hotter than normal. No one is getting burnt. 

After various internet searches I have concluded this is steam flashing, which seems to happen with reduced pressures maybe due to obstructions in the supply side of the heater??

Any suggestions on what this could be, and how to fix?
do you agree with my assessment?

What is the danger of not fixing? Will I flood my house eventually?

Comments

  • DavidSa
    DavidSa Member Posts: 12
    I can’t figure out how to post a video file to show the sounds. 
    thanks in advance. 
    This is a very well curated forum!
  • mattmia2
    mattmia2 Member Posts: 3,170
    How many times has the combustion side been cleaned? When was the last time a combustion analysis was done?
  • DavidSa
    DavidSa Member Posts: 12
    And my last question for now.... I’m thinking to replace this inlet valve in case it is restricted but I can’t figure out what it is ( I would replace it exactly). 
    Any comments?
    l

  • DavidSa
    DavidSa Member Posts: 12
    The question: How many times has the combustion side been cleaned? When was the last time a combustion analysis was done? 

    Answer:  perhaps never. I didn’t ever think to see if that is a thing. 
    I’m going to google that now. 
    Looking through the sight glass I can see something that could look like a hot spot?

    could that cause a problem?




  • DavidSa
    DavidSa Member Posts: 12

  • dopey27177
    dopey27177 Member Posts: 541
    Have you checked the cold water inlet where cold water mixes with hot water to get down to final water temp of 120.

    Jake
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 1,599
    DavidSa said:

    I can’t figure out how to post a video file to show the sounds. 
    thanks in advance. 

    This is a very well curated forum!
    Thanks, @DavidSa. Please upload your video to YouTube or a similar site and then you can share the link here.
    President
    HeatingHelp.com
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,181
    Hi @DavidSa , Do you know what the gpm flow is when your heater is making the sounds? I see that the supply line is crimped PEX with a 90 in it. That will restrict flow into the unit. A test that comes to mind is to get the heater making noise, then reduce the water draw. If it quiets down, it's telling you that pressure in the unit is too low.

    Yours, Larry
    CanuckerPC7060
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,106
    How much pressure is on the boiler Should be 15psi.

    Look at some of the "Mikey Pipes" videos on yo tube. Navien 's are doing very well lot's of bad heat exchangers putting out Co into the house
  • DavidSa
    DavidSa Member Posts: 12
    Thanks for the comments. 
    Here’s a link to YouTube for a video of the sound. 
    It’s really noisy and I feel vibrations in the primary HE outlet. 

  • neilc
    neilc Member Posts: 1,304

    How much pressure is on the boiler Should be 15psi.

    Look at some of the "Mikey Pipes" videos on yo tube. Navien 's are doing very well lot's of bad heat exchangers putting out Co into the house

    I've been following Mike on the tube,
    and been wondering about starting a thread here,
    wondering what this community thinks of that issue,
    and yeah, my parents have one and all the same symptoms.
    sorry for the sidebar OP
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,106
    @neilc

    Can't say I like Mike cause I don't but something seems to be going on with Navien. Don't understand the flue recirculation and bad gaskets. Some of the jobs are bad installs no doubt but not all of them
  • DavidSa
    DavidSa Member Posts: 12
    Have you checked the cold water inlet where cold water mixes with hot water to get down to final water temp of 120. Jake
    I don’t understand the question. 
    I didn’t know the temperature is mixed down to 120. I assumed the heat was controlled to heat it to 120. 

    What would I be looking for?
  • mattmia2
    mattmia2 Member Posts: 3,170
    When does it make the sound?
    Is it only when it is firing and after the burner has been on a while?
    Does it make the sound all the time while it is firing?
    Does it make the sound when the blower is running for pre-purge and post-purge before the gas has even turned on/after it has shut off?
  • DavidSa
    DavidSa Member Posts: 12
    mattmia2 said:
    How many times has the combustion side been cleaned? When was the last time a combustion analysis was done?
    I figured out how to Quote prior responses so I will re-reply to a prior question. 

    Answer: it’s likely never been cleaned in 12 years. I do see a bright orange dot in the sight glass... is that a hot spot. 

    I attempted to google this and didn’t see an obvious way to clean it. 

    Could the combustion side be causing problems?
    What would I look for?
  • mattmia2
    mattmia2 Member Posts: 3,170
    The glowing spot is soot that should be cleaned out, but i don't think that is your problem. overall all of the soot could maybe be restricting the air/gas mix flow and interfere with combustion. Is the flame steady through the sight glass or does it surge and bounce and dance around?

    I would try listening or feeling with a screwdriver used as a stethoscope to see if you can pinpoint where it is coming from. I know some HTP boilers had a backdraft flap in the exhaust that would break off and flop around.
  • DavidSa
    DavidSa Member Posts: 12
    Hi @DavidSa , Do you know what the gpm flow is when your heater is making the sounds? I see that the supply line is crimped PEX with a 90 in it. That will restrict flow into the unit. A test that comes to mind is to get the heater making noise, then reduce the water draw. If it quiets down, it's telling you that pressure in the unit is too low. Yours, Larry
    The unit is at least 12 years old and didn’t make the noises before. It does seem like the noises could be due to restrictions but I think not the PEX specifically as that hasn’t changed recently. 

    I don’t know the flow rates but I just ran a shower and it took a few minutes for the noise to start sporadically. I then added a tap and it went crazy so it seems to be flow rate-related, which likely just means the pressure is too low at higher flow rates?

    if this is the case then I assume I need to look for new pressure restrictions upstream of the HE’s? 

    Unfortunately I can’t figure out a way to measure pressures upstream or downstream of the Navien but I’m gonna look at that again.  

    Is there a way to read the rate off the Navien flow meter?
  • DavidSa
    DavidSa Member Posts: 12
    How much pressure is on the boiler Should be 15psi. Look at some of the "Mikey Pipes" videos on yo tube. Navien 's are doing very well lot's of bad heat exchangers putting out Co into the house
    I don’t know the pressure but I am going to look harder for a spot to add a meter. I assume I need it just downstream of the Navien?

    I looked at a few Mikey vids but haven’t yet found one about Navien. This unit is 12+ yrs old so it has put in its time. 
  • DavidSa
    DavidSa Member Posts: 12
    mattmia2 said:
    When does it make the sound? Is it only when it is firing and after the burner has been on a while? Does it make the sound all the time while it is firing? Does it make the sound when the blower is running for pre-purge and post-purge before the gas has even turned on/after it has shut off?
    It isn’t always consistent but it seems to be generally after the burner has been firing a while, almost certainly never during prepurge and I think not during post purge but not sure. 

    I disconnected power and it ran with no popping so that seems to confirm that it is heat-related. 

    I also tested high and low flow rates and it seems worse at high rate. I don’t have any way to measure specific rates unless Navien can output it. 

    I still haven’t measured pressures but I’m sure supply is in the range of 125psi. 

    I put an infrared gun on the outlet for two different runs and was surprised. I attached videos below. 
    In 1 video the popping started at 75F outlet, up to 95F and the outlet temp never got over 95ish. The blower was cycling higher and lower and the popping is much higher when the blower is lower. 

    The second video is similar but temps were higher at up to 110F and never really below 90F. 

    So this leaves me thinking: 
    - maybe it is a pressure problem: I don’t think the piping is a problem so maybe the master valve or the flow control valve?? 
    - maybe a blower problem. I don’t know how it’s controlled. The popping increases when the blower speed drops. 
    - Maybe it’s a control problem of some kind: bad temp sensor or flow sensor causes havoc with the flow control, gas valve, blower?
    - having steam bubbles at 75C seems odd... there must be some local high-heat thing going on?

    As always, thanks for your comments. 
  • DavidSa
    DavidSa Member Posts: 12
    mattmia2 said:
    The glowing spot is soot that should be cleaned out, but i don't think that is your problem. overall all of the soot could maybe be restricting the air/gas mix flow and interfere with combustion. Is the flame steady through the sight glass or does it surge and bounce and dance around? I would try listening or feeling with a screwdriver used as a stethoscope to see if you can pinpoint where it is coming from. I know some HTP boilers had a backdraft flap in the exhaust that would break off and flop around.
    Most Tankless techs can do a combustion clean out?

    I think the flame is steady.  I don’t really see flames but just a blue sheet of combustion. 

    I have been struggling to figure out where the sound is from. I like the screwdriver stethoscope idea. I’ll try it... tomorrow. 
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