I have a client that called and says his water heater pilot wont stay lit. They suspect its due to the gas furnace when it starts since they are installed right by each other. Is it common for this to happen or does it have to do with the burner being dirty or the thermocouple going out?
Thanks
Without any additional info, I’d guess probably thermocouple.
Does it go out every time furnace comes on AND only when furnace comes on?
I vote thermocouple change it out:D
The other possibility is draft.
It’s pretty classic for a marginal thermocouple. When the furnace fires off, the gas pressure may dip just enough to take the output from a marginal thermocouple below the threshold to keep the gas valve on. For the 6 dollars they cost, I’d replace it anyhow just to not have to consider it in my troubleshooting process, and it will probably solve the matter too. A thermocouple is a regular PM part for a water heater, almost like replacing the furnace filter or the brakes on your car.
I would change the thermocouple First as Marc said gas will dip when the furnace kicks in
They have had the water heater for about 6 years so I would imagine its the thermocouple going out because the pilot started going out a few days ago. I would think this would rule out the possibility of the furnace causing the pilot to go out.
Do I get to vote twice:D:D:D:D
Thanks Guys for all the input, I really appreciate it.
I’ll vote for you. Thermocouple. 
Thermocouple…just changed one out for the same exact reason on my mother’s water heater 2 weeks ago.
Thermocouple for sure.
as a licensed home inspector we are not qualified to recommend specific repairs unless we also hold a license for that trade.
do so at your own expense and possibly jeopardize your livelihood
i’d advise qualified seasonal servicing of both units (HVAC & WH) as there are possibly other issues present that we or they are not aware of…
others are possibly right 
hth
I held a gas Fitter Licence
great, but were you onsite to actually diagnose the problem and any potential for other issues, is all i’m getting at
how are the fittings at my house 
I just suggested it, didn’t repair it . Where i come from a gas fitter do the installation not plumbers Here Plumbers do the the gas work . I used to work on everything from a wall heater to Boilers you could stand in the fire box.
I too recommend a license contractor do any work on systems. I also recommend serve every year which i have never seen down here just doesn’t happen
You need to change out the 90 in the SE corner has excessive rust.:D:D
They were not actual paying clients their my parents who just asked me about the problem and I did my research here on the board.
Let us know what you find Steven
Good luck
Will do Wayne, Thanks!