Hi, I have a Apollo Hydreswirl water tank which may be 10-15 years old. During the past seven years that I have lived in the house I had the Thermostat set at "hot" position & I always had hot water.
But, for the past 5-6 months I have to set the thermostat at Hot B to have hot water & even at that setting I don't have that much hot water.
I got a experienced Plumber & he suggested to change the dip tube. Do you think this will solve the problem or what is your solution.
On the 3rd of February I emptied the tank & when the tank was half empty I poured 9 ltrs of vinegar & kept it for 45 mts & flushed it out. I didn't see a drop of calcium coming out.

Checking the dip tube would be a good place to start. If the dip tube is in good working order, and there is no sediment buildup in the water heater, the gas valve/thermostat may be malfunctioning. If that is the case, with a water heater that old, I would look toward a complete new water heater.