Hot water using the boiler
Using my boiler that has a heating coil and is plumbed into the hot water tank– My hot water is coming out brown looking and sulfur smelling but not bad –just brown colored. Can the coil be bad?
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The coil certainly can be bad . How old is this boiler and what make , model is it ?
Having to maintain a jacket temp all year to insure DHW is also not such a good thing .
It sounds like you are describing a tankless coil. As Richard pointed out, your coil could certainly be bad.
No one recommends using tankless coils any more to make domestic hot water; keeping a boiler up to temperature for 24 hours a day during the summer wastes a lot of energy. You should look into installing an indirect water heater -- basically a tank with a heat-exchange coil. This indirect tank can be set up like a separate hydronic zone with its own circulator, controlled by an aquastat. With an indirect tank, the boiler doesn't have to maintain a high temperature for 24 hours a day.
Not only are the standby losses of tankless coil boiler very high, to get reasonable hot water performance typically requires 3-4x oversizing of the boiler for the space heating load, leading to dismally low "as-used" AFUE efficiency, a combination of cycling losses & standby loss.
Rather than replacing a bad coil it's usually better to either install an indirect fired hot water heater operated as another zone off the boiler, or install a heat pump/electric hybrid hot water heater, and install a heat-purging economizer control on the oversized boiler.