A friend of mine tells me that every couple of months when he opens up the hot side of any faucet he gets nothing. no water, no air, nothing.He says if he opens the relief valve on the water heater he also gets nothing. But after opening relief valve he can then go to any faucet and get hot water. It doesn't happen again for a couple of months. Could it be a problem with the flexible line on hot side or possibly a dip tube problem? It is a natural gas heater.
that relief should blow off. anytime it is manually lifted he need to flush it out and remove the hot pipe and check that dip rod the hot water rises up.....that is street pressure from the cold side something is floating inside that tank to hold back 50PSI house pressure or even more....might also might have mineral buildup on the hot line out....find out when he opens the drain with a hose connected that also should be cold water pressure if thats blocked the tank is fouled up