I have a coil indirect hot water tank heated by oil boiler. There are
two pumps, one for the rads and one for the hot water. recently I have
been getting very tepid water no mater how long the boiler runs. The
thermostat on teh tank is set to 60 and the boiler stat is at 70.

The top feed pipe into the heat exchanger is very hot but the bottom
return pipe is freezing. I would have thought the return would have
had some heat. I have tied upping the pump speed with no luck.

Does this sound like the exchanger is blocked with sludge or maybe an
air-lock. Any ideas what it might be or how to fix it.


Peter Hawkins