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Hobart C44AW dishwasher issuenafets47 replied 3 years, 3 months ago 6 Members · 35 Replies
oliveroMemberMarch 1, 2020 at 11:45 am
I don't quite see how RTV sealant or any type of insulator could reach a higher temp than what it's submerged in.
Delayed ignition or “barking” would be caused by either too much of either air or fuel or not enough of either OR the igniter not sparking enough or heating up enough (depending on the style) and so the chamber has time to build up gas and create a “bark”.
Having already replaced the high limit, with a gas burner below, the only reason I could imagine is that somehow the cap tube from the high limit is getting hit by the flame or the exhaust of the burners, there's simply no way it's being caused by the water, UNLESS there is an intremittent thermostat fault that allows it to go higher at certain times, but from what I understood, Nafets has been there, probe in hand measuring the temp and seen it to match the installed temp gauge and then have the hi limit trip, so that to me; indicates some other sort of heat source getting at that cap tube.
What's your take on that? I haven't worked on any gas dishwashers before so I don't know enough about them to say where and how but just theoretically.
nafets47MemberMarch 1, 2020 at 4:15 pm
Yes. Like olivero was stating, the temp on the gauge is the exact temp in the wash tank. Just so it is understood, the high limit that is tripping is from the wash tank not the booster.
Since I am not in front of the dishwasher all day long and what was communicated to me by the person who is, is that the washer does not go past the 160* temp that cuts off the heat. I also verified that the setting of the electronics on top of the unit only requests temp to 160 then shuts off the ignitor.
What I was thinking might be occurring, is that the gas air mixture is not correct (which is evident by the “barking”) and this sudden surge of heat is coming into the ignition box when it “catches” and is hitting the small amount of tubing that is exposed on the high limit (the remainder is in the immersion tube in the wash tank). Since I also found evidence of some burn residue on the new high limit I just installed. Does this seem accurate?
fixbearMemberMarch 1, 2020 at 6:30 pm
I don’t quite see how RTV sealant or any type of insulator could reach a higher temp than what it’s submerged in.
When there is any form of insulation on a sensor it delays the reading. Yes, eventually it will reach the liquid temp, but heat saturation of the heat exchanger will make it rise higher than design. It will also call for heat later and you will see larger drifts in the temp than normal.
so that to me; indicates some other sort of heat source getting at that cap tube.
What’s your take on that?
Does the cap tube slide into a tube fastened to the heat ex changer? Look for minerals between them acting as a heat sink
UNLESS there is an intremittent thermostat fault that allows it to go higher at certain times
That's exactly what I was saying. But the question of does it have a rinse booster or not has not been answered. You may be looking at the wrong limit.
fixbearMemberMarch 1, 2020 at 6:38 pm
For sanitation purposes the rinse is normally 180F Hobart calls 160 wash as a min.
Since I also found evidence of some burn residue on the new high limit I just installed. Does this seem accurate?
Ouch. That means your new burner gasket is leaking. And depending on how much is exposed, yes.
oliveroMemberMarch 1, 2020 at 8:21 pm
Fixbear, I still don't believe it could rise that much, we're talking latent heat upwards of 40*F, I've never seen that, especially not on an insulator.
I think the flame or burn marks on the high limit cap tube is the main give away at this point, the so called “smoking gun” that's what I would be thinking.
It's the wash tank high limit that's tripping, the booster is just for sanitizing, it was mentioned in an earlier post by Nafets.
fixbearMemberMarch 2, 2020 at 7:18 am
That all depends on how clean the heat exchanger is. I've seen some with a lot of mineral buildup from a lack of de-limning..
oliveroMemberMarch 2, 2020 at 11:41 am
I could see the HE insulating the heat but for it to transfer is what I have a hard time believing. I could see the source of the heat overheating but this is for the water, so that latent heat would have to transfer through the HE and into the water, latent which is what I've never seen, personally. I'm not saying it's impossible, just that I've never seen it.
fixbearMemberMarch 2, 2020 at 4:26 pm
Olivero, It has to do with time and K value. If there is a material between the sensor and the water that has a high K value the time for the heat to cross to the sensor will be longer than the time of a low K barier. This means that the sensor will be late cutting off the heat call and overrun will happen. Bad enough that Hobart uses a large sensor casing to make it strong, and it already has a mass inside if that stainless probe that slows the sensing. Add anything else and the temp width will increase even more.. The actual thermocouple is embedded in a compound to transmit the heat. But even that has a K value. But very low. Like a heat sink compound.
oliveroMemberMarch 2, 2020 at 5:53 pm
That I can understand, I thought the hi limit being covered in an insulator is what we discussed. I can understand the thermostat being insulated and then not reading the temp has passed it's setpoint and then tripping the hi limit, that I believe and I have seen that.
fixbearMemberMarch 3, 2020 at 12:14 pm
The same thing can happen with a cap tube sensing that has been pinched or kinked. It can still function, but very slowly both open and closed.
oliveroMemberMarch 3, 2020 at 1:54 pm
Yes, that makes sense. I think there was a confusion on my end in terms of what was being discussed.
nafets47MemberMarch 2, 2020 at 11:17 am
The water coming into the washer is 0 hardness if that means anything. The entire building has the water softened to 0 before it enters the pipes.
Also another piece of data, and something that I am going to address as soon as my tool is returned to me, is that the high limit was reset last night and then the washer told me that it started “barking” and then wouldn't get to temp. I check this morning and it was again tripped.
So this I believe is now the issue to resolve. I will have that point fixed this afternoon and let everyone know tomorrow or tonight depending what is the result.
fixbearMemberMarch 2, 2020 at 4:32 pm
“0” ? what is it, distilled or RO. Your machine need at least a 6 for longevity.Have you chemical supplier test it to be sure. That's pertly low and will cause heat exchanger problems.
nafets47MemberMarch 2, 2020 at 5:42 pm
We have a water softener system which uses salt. The chemical provider worked out the appropriate chemical for our system and has been working well.
We have a water treatment company come out once a month to check chemicals for my chiller loop on the property and it is always 0 water hardness. Believe it or not this washer has been running for 13 years for two work shifts every day. Pretty crazy.
Anyway, using a manometer the gas was checked and was 3.4 not 3.2 like it should be. The washer was barking every time I fired it up checking the gas until it hit 3.2. Now no noise and fires up on the first try. So we shall see.
nafets47MemberMarch 4, 2020 at 10:52 am
An occasional “bark” afterwards. Took apart the blower fan and found some loose paint inhibiting the blower from moving freely. Cleaned that up, removed any and all barking and no longer tripping high limit.
So looks like this one is a DONE.
fixbearMemberMarch 6, 2020 at 1:33 pm
I suspected that you had something restricting the air. Glad you got it.
nafets47MemberMarch 6, 2020 at 4:54 pm
Yea, I did too originally. I spun the blower by hand and didn't hear or feel anything inhibiting movement. Only after taking it apart did I find loose paint.
Thanks, me too and so is the guy who washes dishes.
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