Keep turning the thermostat up

[simon10]

We have a gas fired Smith 40 gal water heater about 6 years into its 10 year warranty. The unit has never given any trouble and never runs out of HW (only 2 people taking showers). Since the weather got colder I notice that when taking a morning shower (no HW use all night) the shower mixer valve needs to be set almost all the way over to hot, rather than mid way between warm and not.
I "fixed" the problem by turning up the WH thermostat, now it's midway between B and C settings.
The same thing happened last winter but never an issue when the tank was newer, even though winters were colder (tank in basement). Last year I was able to turn the thermostat down again when the weather warmed up.
The burner appears to fire up as normal after the shower has been running a couple of minutes.
Anyone any idea what's going on with this WH?

 

[frodo]

I think the problem is the shower mixing valve and not the w/h

are you noticing any temp change any where else in the house?

 

[Mr_David]

Hmmm, Colder weather = water colder. Colder water mixing with hot water. Need more hot water to account for colder water maybe?

 

[Chris]

Mine does something similar, after sitting all night or all day I will have to crank the hot water but then if another shower is taken within the next couple hours it will be scalding at the same setting. Almost as if the water in the tank is cooling after sitting for some time.

 

[simon10]

I don't think it's the mixing valve as I ran the hot faucet first thing the other morning it's not as hot as usual, but just as Chris said when the next person showers it's too hot with the mixer in the same position.
It seems totally logical that the basement is cooler in the winter so the tank cools more over night than it does in the summer, but not enough to fire the burner, resulting in cooler water for that first shower. That combined with cooler cold water hence the need to crank up the mixing valve.
What I don't understand is why this has only happened the last 2 winters and is it an indication that some components need to be replaced.

 

[Chris]

I live in So Cal so my tempts are never cold and mine does it daily, winter or summer.

 

[frodo]

where do you live simon ? do you live in extreme cold weather ?

get an insulation blanket http://screencast.com/t/zFCInjNe

wrap the heater, also, insulate your pipes, see if that helps.

i still think its the mixing valve, but eliminate the insulation first. I am often wrong, just ask my wife



try something, turn off the valve on the water heater. then, go around the house, and 1 at a time
open the HOT valve on your faucets, see if you have any water., 1 at a time,, go outside, open the hose bibs
see if you have cold to your hb....humor me, looking for a crossed cold on a hot manifold
,,

 

[simon10]

I live in Long Island NY.
The layout is is really simple, all pipe runs are visible in the basement and bathrooms are directly above, so nothing is crossed.
I realize the tank could be insulated, but I'm trying to understand why this is has only been an issue in the last couple of years and nothing has changed. The mixing valve is Grohe pressure balanced by the way.

 

[Caduceus]

A flush-n-fill of your water heater always helps to remove sediment that could be building up on the bottom and slowing the heat exchange between the burner and the water in the tank. Cleaning the combustion chamber/burner assembly can improve performance, too.