I have a problem that has all 3 plumbers I've spoken to wanting to break into my walls and I'm feeling a little desperate... Hot water worked fine then was turned off because people moved out. A month later (now) people moved in again and turned on the hot water heater - which apparently caused something to make a blockage in the hot water pipe. I would think that there would be a product that would "eat through" a blockage in the fresh water line so that walls didn't have to be torn out... or a snake that could be used? Does anyone have any ideas or does the slight trickle of hot water that comes out mean my wall has to come out too?

Before tearing walls out, a little more information about what is or is not happening?

Do you not have water (hot or cold) out the hot side of any faucet?

If you open the drain valve to the water heater do you get water out (under force)?

Does the water heater have heat trap nipples?

Does the hot water out pipe feel warm at the water heater?

Thank you for your reply! There is cold water on the cold side of the faucet in the bathroom sink and in the bathtub.
There is hot water that will trickle out of the hot water side if the trickle has been allowed to run for a few minutes.
Not much hot water but a trickle/stream - no larger than a pencil in size though.
We have NOT opened the drain valve to the hot water heater to know if we get water out under force.
We do have hot water in the kitchen sink and in the other bathroom in the sink and shower that doesn't seem to have a flow problem at all.
The hot water heater is on the same side of the house with the working shower/sink and kitchen however - The bathroom that has no hot water (or a trickle of hot water after awhile) is on the opposite side of the house.
As we have never heard of a heat trap nipple - I'm going to venture a guess here and say no.
Yes the hot water pipe out at the hot water heater is warm 2 1/2 feet from the bathtub the galvanized pipe get so hot you can barely touch it, about 5 1/2 feet from the sink is the same - hot galvanized pipe.
The plumbing is about 40 years old (as is the house)recently renovated - everything except the plumbing - because there had not ever been a problem before with the plumbing and the inspection didn't indicate any problems.
The house has been lived in for a year straight - and for about 40 years before that, then empty about a month and reoccupied - Presto - problem!

Yes the hot water pipe out at the hot water heater is warm 2 1/2 feet from the bathtub the galvanized pipe get so hot you can barely touch it, about 5 1/2 feet from the sink is the same - hot galvanized pipe.

Base on that I suggest
1. Turning off the cold water input to the water heater.
2. Remove the hot water stop valve under the sink.
3. Hold a pail under the hot water pipe.
4. Have someone turn on the cold water stop valve at the water heater briefly (few seconds). See what kind of flow you get out of the hot water pipe under the sink..

Suspect that turning off the water for a period of time, then turning it back on, moved some rust and debris in th old galvanized pipes to the stop valve under the sink.

If you find you have a good flow out of the pipe, replace the stop valve under the sink with a new valve.