I have a "Thermia" geothermal unit installed in our house in 1995. This unit has hot water on demand option. During this time it performed satisfactory. At the beginning of July 2010 I had a "LOW PRESSURE FAULT" light on the system. I contacted a repairman and he changed a "by pass valve". After a few days I started having a "HIGH PRESSURE FAULT" light, and would not heat water anymore. The contractor that I did call did not understand my system very well and told me to contact some other contractor that was familiar with my system. I called one recommended by a friend, he came worked on the system for about 2 hours, could not recreate the problem, told me to clean the coil, and that otherwise everything was fine and left. Between the two contractors it cost me $1200.00. Two day later the problem came back again, so far he has not been able to come back. I can reset it, it runs ok for a few days then I get the light again. I hope some one can help me with first finding a good, reliable, expert service company in my area, Caledon Ontario, Canada. And second on how and what product to use, to clean the coil. It is very difficult to get at the coil.