El Penguini wrote:

I have a potable hot water system that uses the third zone off of my furnace
to heat a coil in a storage tank.

While the water is hot, it isn't hot enough for my liking.

Can someone give me a clue on how this system works, and what settings I
should be looking for?

Thanks
Peter

That is known as indirect fired domestic hot water.

The first question is what is the delivered water temperature you are
getting? It should not be above 130 degrees for safety.

The output of this indirect fired storage tank should have a tempering
valve which mixes cold water in with the hot output of the tank to
maintain this 130 degree limit. The tempering valve will have three
connections and usually a black knob at one end which can be used to
adjust the output temperature. This would be the first place to check,
both the adjustment and the valve itself as they can go bad.

The indirect fired storage tank should have a temperature control on it
that is used to request heat for it's "zone" when the tank temp is low.
If there is a proper tempering valve on the tanks output then this
control can be set fairly high, close to the boilers operating temp, if
no tempering valve then this control has to be set to the 130 degree
limit or lower.

If the actually boiler operating temp is lower than 130 degrees you
likely have a problem there since that is abnormally low. 160 - 180
degrees is more typical for a boiler operating temp.

Summary: The indirect fired DHW tank operates as a heating zone from the
main boiler. It has it's own thermostat which would be set between 130
and 180 degrees depending on whether there is a tempering valve on it's
output. It should have a temperature gauge so you can see the current
tank temp. If it is sufficiently hot and the delivered hot water temp is
still too low, the tempering valve is suspect.

Pete C.