Goodmorning to all. My bathroom water heater mulfunctions frequently (every 2 months or so) in the sense that it burns the thermostat and hence cannot heat the water. Instead of replacing the thermostat all the time or changing the heater itself, does anyone have any idea what the problem might be?

Sounds like you have one of those difficult to find intermittent shorts. Carefully examine any wiring you have access to looking for bare or burned spots that could short to the metal parts of the heater. Maybe remove the elements and look for discolored places from a short. If you find a suspicious spot on on an element, replace it and you may have fixed the problem.

You might compare the breaker with the rating of the heater and the wiring. A 30 amp breaker should be wired up with #10 wire and be feeding less than a 6000 watt heater. If a smaller breaker will carry 80% of the load, it would be more likely to trip before the thermostat burned up. Sometimes people make the dangerous substitution of a larger breaker when there are problems. Next problem, something burns up, sometimes the whole house. Also, make sure the thermostat is rated for what the heater draws.

Please give us more details. The brand and type of water heater. Instant? Regular? Have you contacted the manufacture with your complaint? Regards, Tom