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Old 02-10-2016, 07:26 PM   #1
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Giant UG40 HWHTR hi limit tripping


I have a Giant UG40 natural gas hot water heater 5 years old. The hi limit sensor keeps tripping. I have:
- cleaned out the burner area
- replaced the hi limit sensor
- put on a new thermal couple.
- today I put in a new gas control valve (the old one had calcium build up on the water temperature probe.

Still tripping. Arghhhh!

I seem to have good draft, the chimney is not blocked, I even opened the window in the utility room. Have a nice blue flame.

Any suggestions?

I think the hi-limit switch trips at 250. Problem is it kicks off the pilot so you have to manually restart the puppy.
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Old 02-10-2016, 07:43 PM   #2
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Is it conventional flue or power vent?

100 percent sure no rodents or snow ect., interfering with draft. You replaced just about everything. lol.
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Old 02-10-2016, 07:54 PM   #3
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Jmon,it is conventional. I went on the roof, pulled the liner hood and checked the liner. I checked the exhaust piping from the HWHTR to the liner -- clear.

Next?
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Old 02-10-2016, 07:59 PM   #4
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Thank you for that information Mac and welcome to the forum.

If you could, please post a couple pictures of your water heater set-up. Thanks.

I responded to your post, you should be able to post pics now. Once again, thank you.
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Old 02-11-2016, 03:38 AM   #5
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Jmon, here is a picture, unit is at my daughters and she did not capture a picture of the exhaust pipe but the chimney is about 2.5' behind the unit so travel is not that far.
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Giant UG40 HWHTR hi limit tripping-670-hwhtr01.jpg  
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Old 02-11-2016, 10:15 AM   #6
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Thanks for the picture Mac. Really could use another one of the flue area when you get a chance. Thanks.

Can't tell from picture, but does anything else use the vent? Does flue rise or is it level going out? Below picture is just an example of exhaust vent.

Another thought; This may have nothing to do with your problem, but most water heaters have a filter in the combustion chamber somewhere that can get plugged and may affect combustion. They are usually very tricky to get at (of course, right). May have to get your owners manual out and look at the exploded view on that model and see if you have one. If no owners manual, you can google your model number and download it free.

Some are all the way on the bottom, yours may be on the side where the make up air vent is located towards the bottom. Make sure that it's clean. I use an air compressor or shop vac to clean them depending on how difficult it is to get to them.


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Old 02-11-2016, 10:15 AM   #7
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Hope you get it figured out soon so your daughter will be happy and so will you. I know it must be very frustrating spending all that money on new parts and it still keeps tripping. The worst part of it, it may something simple that's causing it.

We have excellent plumbers and hvac techs with a lot of experience on this forum that may be able to give you more advice/suggestions. Please wait for one of them to respond. Thank you.
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Old 02-11-2016, 11:07 AM   #8
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Thanks for you assistance Jmon.

The HWHTR flue is all by itself. The furnace is a hi-ef and has both its intake and exhaust on the side of the house. The vent go vertical about 14" then horizontal about 2.5' then into a liner. That I think is 5 or 6".

You can see in my picture the outer shell of the HWHTR has a air vent just below the dip tube, but that just gets into the in-chamber -- there is no filter. I think the combustion air has to flow down and under the tank and up to the burner.

Maybe I will try the compressor and give her a good blowing out.

Regards, Mac
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Old 02-15-2016, 01:31 PM   #9
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I blew out the combustion area and the screen on the bottom the best I could then vacuumed again.
This unit's exhaust was feeding into a 6" liner, so I also replaced that with a 4" liner. Still tripping!.
I am trying to get access to a thermal gun, but I tested the metal with a digital meat thermometer (please don't laugh) and the temperature says it is kicking out at is 180F. If I bypass the hi limit and the temperature stays constant at around 202 to 204. Does that sound right?
When I bypass the hi limit HWHTR functions normally, but I do not want to leave it in that state.
Maybe I have a 2 faulty hi limit sensors!
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Old 02-15-2016, 02:01 PM   #10
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does that unit have screens at the bottom in case of flammable vapor? if so they need to be cleaned out and vacuumed, they will cut the heater off for lack of air into the combustion chamber..you see the black ring on the bottom..that should be a screened plastic..
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Old 02-15-2016, 06:30 PM   #11
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Yes, there is a screen at the bottom of the combustion chamber, I vacuumed from the top and blue compressed are into the cavity underneath it.

Maybe if I pull the burner out I can lift that up and give it a better cleaning-- would that work?
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Old 02-15-2016, 07:21 PM   #12
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Quote:
Originally Posted by macnec View Post
Maybe if I pull the burner out I can lift that up and give it a better cleaning-- would that work?
Yes. That's exactly how I have to get to mine. The whole burner assy. has to come out and then I can get to my filter. It's pita, but can be done.
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