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I have an older AO HW200 M 890 series (standing pilot) that…

Customer Question
I have an older...

I have an older AO Smith HW200 M 890 series (standing pilot) that we cannot hold the pilot. The t'couple puts out over 30 mv. If we jump out the wires going to the protector switch sometimes it works sometimes it doesn't. We have cleaned the pilot, replaced the t'couple, replaced the gas valve and still does not remain working on a consistent basis. Do you have any advice? I am uncertain on how to properly diagnose the operation of the t'couple and the wiring to and from the protector switch. Any input?

Contractor's Assistant: I'll do all I can to help. How long have you been dealing with this?

Over a week

Contractor's Assistant: Do you plan on doing the work yourself?

Yes either myself or one of my technicians, I am the service manager for a commercial sized mechanical contractor. I have looked at this along with two other technicians. As soon as we think we made progress something different occurs.

Contractor's Assistant: Anything else we should know to help you best?

As it stands now, we removed the replacement gas valve because it wouldn't hold the pilot at any time and re-installed the original valve with a typical t'couple. (no connections for protector switch). It ran overnight that way. This is supplying HW for an apartment complex.

Submitted: 9 months ago.Category: HVAC
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Answered in 32 minutes by:
12/14/2017
HVAC Technician: airheatman, HVAC Technician replied 9 months ago
airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 9,542
Experience: Furnace, A/C and heat pump specialist.
Verified

Most of these protector switches were manually reset. Do you have an auto reset switch?

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Customer reply replied 9 months ago
No, it is manual reset and has not tripped. Continuity test shows closed.
HVAC Technician: airheatman, HVAC Technician replied 9 months ago

OK that is what I thought.So since it is not tripping and the fact you jumped it did not completely solve, we can pretty much rule the protector switch out as being our culprit.

Since we are having the same issue with two different gas valves, that sort of leads us to doubt the valve is the issue.

THis leaves the thermocouple and gas pressure as I don't see any other components on the standing pilot, correct?

Have you actually tried replacing , not just cleaning the thermocouple?

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HVAC Technician: airheatman, HVAC Technician replied 9 months ago

OK just re read and see you cleaned pilot and replaced thermocouple

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HVAC Technician: airheatman, HVAC Technician replied 9 months ago

Are there any other components on this heater other than what we I just mentioned. (Gas valve,protector switch,pilot and thermocouple)?

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Customer reply replied 9 months ago
No sir
HVAC Technician: airheatman, HVAC Technician replied 9 months ago

OK it appears you have tested everything and under ideal circumstances everything works.

This means something has to be changing that is causing us to lose pilot.

The two most common external issues are gas pressure supply and wind.

Does there seem to be anything of significance that is changing when it goes off? (high winds outside, extremely low freezing outdoor temps,opening and closing door in location of water heater that could create a draft,high usage of other gas appliances such as furnace)?

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Customer reply replied 9 months ago
I am sorry none of those suggests apply. This is why it is so baffling to me. I wonder if you can answer this question. When I read the output of the t'couple from the terminal closest to the pilot to ground I read 30 mv. With a jumper across the terminals and I read from the other terminal (closest to the gas valve) to ground, I read 2 mv. Does this tell you anything?
HVAC Technician: airheatman, HVAC Technician replied 9 months ago

THat really doesn't tell me anything.I have never had any reason to put a jumper across them in troubleshooting.

Have you ever been able to get to "NOT relight" and have the 30mv at valve or when we have the 30mv does it always light then just go back out later?

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Customer reply replied 9 months ago
We have always been able to relight the pilot. The thermocouple has always produced the 30 mv but the pilot has not always been held on once the gas valve knob has been released. It may work for awhile but then fails. For instance, it worked from 3:00pm-6:00pm. Relit at 6:00pm and would not hold, relit again (second try) and held to 9:00am the following morning.
HVAC Technician: airheatman, HVAC Technician replied 9 months ago

I would try another valve but if original does not have the witch, use one that does not

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Customer reply replied 9 months ago
I do not understand your response
HVAC Technician: airheatman, HVAC Technician replied 9 months ago

You stated original gas valve did not have the place to connect the protector switch yes?

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Customer reply replied 9 months ago
No I did not say that. The protector switch attaches to the thermocouple anyways not the gas valve. We have not altered the situation from what it was originally, only replaced components with what was there. I feel you are in the same position as I was before we conversed. Guessing that it is a gas valve issue even though it is a new gas valve. Agree? I suppose we could have caught a bad valve.
HVAC Technician: airheatman, HVAC Technician replied 9 months ago

I understand. In your original post you stated " re-installed the original valve with a typical t'couple. (no connections for protector switch)." is why I thought you had made a change.

Lets try a new valve and see .It is possible you got a bad one .

The only other thing I could imagine would be a venting issue letting downdraft blow out the pilot.

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Customer reply replied 9 months ago
Down draft is not the issue. We can watch a perfectly good pilot flame drop immediately out when releasing the gas valve knob.
Can this conversation be picked up at a later date because our local supplier does not have another valve in stock, has to be ordered?
HVAC Technician: airheatman, HVAC Technician replied 9 months ago

Absolutely.Just come back to the question any time

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Customer reply replied 9 months ago
Thank you!
HVAC Technician: airheatman, HVAC Technician replied 9 months ago

Good luck,Hope the valve solves

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