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The pilot in my gas water heater (Aquamax 205) has been going out sporadically over the last 2 weeks. Yesterday, I replaced the thermocouple with a universal thermocouple and cleaned out the dust and soot from the burner area.

After installation, I also did the detergent test to make sure the gas connections are secure and not leaking.

I lighted the pilot and it appeared to work fine. A few hours later, I checked the pilot and it was out, so I relighted it. I got up this morning and checked it again and the pilot was out again.

The water heater was working really well with no issues before this happened.

What could be causing this?

Edit: I relighted the pilot on Sunday morning and monitored it throughout the day. The last time the hot water was used was at around 8PM on Sunday and it was still working properly.

This morning (Monday) the pilot was out again and I relighted it.

Edit 2: Tonight, I checked the pilot and it was still lit. However, after 2 people took showers at the same time (which probably cause the burner to kick in), the pilot went out. I am not sure whether it went out when the burner was trying to light up or when the burner turned off. After relighting the pilot again, the burner started up.

  • Is the thermocouple in the flame so it gets the most heat? The flame causes the thermocouple to generate a few milli volts of electricity, a weak flame or misaligned thermocouple could cause the problem. Is the gas valve end of the thermocouple seated snugly? – Tyson Dec 11 '16 at 1:08
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    Is there an intact weather cap on the vent pipe? Wind can whistle down and blow the pilot out. I have also seen strange things with rain getting in, like burner holes plugged with mineral deposits right near the pilot so as to cause small explosive ignition when the gas valve opens, due to delayed ignition, which blows out the pilot. – Jimmy Fix-it Dec 11 '16 at 6:26
  • I've updated my post with more observations. Yes the thermocouple is in the flame and the gas valve of the thermocouple is sealed tightly. The unit does not appear to have a vent pipe. This is what it looks like: i.imgur.com/RM8CoFc.jpg – F21 Dec 11 '16 at 21:22
  • Replaced Pilot assembly last week as pilot went out when burner shut off. Today I replaced the temperature control valve. Same thing, lit pilot, burner came on the after a heat cycle burner shut off as well as pilot. Trying an immediate restart only igniter worked after about 4 or 5 minutes was able to light the pilot. Then the whole episode repeated. I’ve checked for air restrictions seem okay there. No I’ll lean on the gas company a bit or if someone experienced the same issue and resolved it would be glad to hear from you. – Rusty Ferrell Nov 27 '18 at 20:16
  • I have seen the op's answer several times that's why we put drip legs on gas supply lines but, would have thought Jimmy fix-it comment was the same as I was thinking+ – Ed Beal Nov 27 '18 at 21:02
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I reinstalled the pilot and cleaned out the burner and related assemblies and the pilot was only going out in the morning.

The issue turned out to be because we are still on a low-pressure gas system, which is susceptible to condensation and water seeping into the natural gas service pipes. The guys from my gas distributor pumped all the water out of the pipes and it's been fine since.

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If the pilot will lit but goes out after it reaches the temperature, it is the control valve. It happened to me. After the plumber replaced the control valve then it stays lit. You will have to order the control valve from the manufacturer.

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