only warm water from hot water taps

[brent]

Hi all, here's a real headscratcher for you pros out there. A few weeks ago we suddenly woke up to lukewarm water but not hot. Every hottap in the house was the same, you turn it on, get hot water for a few seconds, quickly fading to only lukewarm. This was the same be it the washing machine, the tub faucet, the kitchen faucet, etc. Cold water taps still gave you cold water.
However, I quickly realized that I could still get hot water from certain taps as long as I turned a corresponding hot water tap on elsewhere. For example, we want to have a hot shower, we just turn on the hot water tap in the sink beside it. As long as the water in the sink is running, we could have a nice shower. There are other 'matches' as well in the house. Washing a load of clothes set to hot gives you hot water in the shower as well, as long as the washer is filling. This will also give hot water to the upstairs kitchen sink, but only if I turn the sink tap to less than half, otherwise is seems to offset the pressure and goes back to lukewarm. I can get my upstairs bathroom sink to run scalding hot water as long as I turn the hot water tap on in the tub next to it but I can never get hot water to the tub no matter what tap I turn on in the house.
A plumbing buddy thinks it might be the 'diptube' in the hot water heater. Apparently it may have cracked and somehow this offsets the displacement of the cold water as the hot is being directed to the pipes. I really have no idea but I'm thinking I'll likely have to replace the heater. I have noticed that If I turn the temperature setting to anything except HIGH the igniter will never kick in so obviously the heater does have some issues. Any advice appreciated, it'll cost me a bundle to replace the heater as we've recently had new venting laws come into effect that will force me to have my furnace piping revented to fit the new codes and new heaters, likely about $1000.
Thanx
Brent

[LazyPup]

I woud have to agree with your plumber, it sounds like a crack in the dip tube.

Under normal circumstances as water is drawn out of the water heater and equal volume enters the water heater via the cold water inlet port on top. As the water enters the water heater it is carried to the bottom of the tank via the dip tube before actually entering the tank.

Water will always follow the path of least resistance, therefore if a crack occurs in the dip tube the incoming cold water will enter the tank into the dip tube then leak out the crack and pass over to the hot water discharge port before it has had adequate time to be heated. The end result is the amount of water leaking out of the dip tube and taking the short path across the top of the heater will dilute the hot water from the tank and results in luke warm water coming from the tank.

When a second faucett is opened the volume of flow is now greater than what can pass through the crack so some of the water is now taking the short path across the top and the remaining volume must by necessity go to the bottom of the tank via the dip tube, thus pushing hot water up in the normal manner.

In this situation the easiest and least expensive solution is to replace the dip tube.

In a worst case scenario where you either cannot get a new dip tube or cannot get the old dip tube out there is another alternative that is seldom used but will work fine. Remove the drain valve from the bottom of the tank then install a brass nipple and a brass tee with the side port of the tee pointing upward. You then replace the drain valve on the end of the tee and connect the cold water input line to the side port of the tee. You then cap the cold water input port on the top of the tank and you back in business.