Vaillant F75-W-45 tankless hot water furnace. I am having a problem getting and keeping hot water in shower. Have to turn up thermostat to run furnace to keep hot water for shower. Furnace runs well and is serviced yearly. Heat works fine (fhw baseboard). I was told I needed to replace tankless coil as it had deteriorated from our well water. Replaced tempering valve in June '07. Other option is to install indirect water heater by furnace for @ $1800.00. Local plumbing supplier has coil and gasket in stock for $245.00. I can do this job myself even if any bolts snap during repair. Can drill and tap with no problem. Will coil come out through front of furnace with control head? Or out through top?

If you are capable of doing all the other work what difference does it make where it comes out from. You are smart enough to fix it and fixing it is a lot cheaper than anything else. Have at it. You will be done sooner than you think. BTW you have to take the top off because of the flue etc. But the exchanger tilts out from the front. You will have to wiggle it a bit.