I am installing a radiant floor heating system fed from a big solar storage/drainback tank, preferably without a heat exchanger. I need help with the controls. This is for a rental house in Big Bear Lake, CA, only steps from the ski slopes. It rents for over $500/night in high season, and I’m willing to give away three consecutive nights for the best answer to my control question. I plan on replacing the old water heater and furnace for a system that is heated from a Triangle Tube Combi Mod/Com Boiler and a drainback solar system fed by about 40 evacuated tubes, as I have decent solar access. Built in 1981, I plan on replacing all the aluminum windows and doors, and adding at least 4” of rigid insulation to all walls and the roof of this square 2000 sq ft house. The first floor (mud room, laundry, bathroom, 2 bedrooms) will get pex inside gypcrete and the 2nd floor with cathedral ceilings (great room, kitchen, bathroom, 2 bedrooms) will get warmboard. Although this is my first floor heating system, I am a contractor with experience in installing apartment drainback systems, building my own 200 to 400 gallon, unpressurized solar storage/drainback tanks. DHW will be preheated in this tank through a 100’ CSST (corrugated stainless steel) heat exchanger, then goes to a boiler’s separate DHW passages and on to faucets. I would prefer to use the same water that goes to the solar collectors for use in the floor heating system (instead of using a heat exchanger) for more performance and no need for a separate expansion tank. The solar tank temp will get up to 150 degrees F, so I plan on using a 3 way mixing valve to reduce temps to the floor heating system. I also want to use outdoor reset to change ‘Supply’ setpoint temperature. For simplicity, the DHW line along with the drainback lines are not depicted in the attached diagram. I plan on using a Grundfos Alpha (stainless, pressure regulated) for the floor heating system, feeding into manifolds with thermostat controlled actuators. This ‘Demand’ pump (P1) must be running before either ‘Supply’ pump (P2 or P3) is allowed to start. 1) If Demand’s return line temp is less than the tank temp, then turn on Solar Supply Pump (P2). 2) If the return line temp is still not up to the setpoint (controlled by outdoor reset) after leaving the solar tank, then turn on mod/com boiler and Boiler Supply Pump (P3). Any advice on what LOW COST control(s) to use for this system would be appreciated.

We have owned our Eichler for 5+ years and during that time seen the heating efficiency of the radiant heating system go down. Nowadays, it is not able to hold the house temperature at even 63F. In the past it did much better. In examining the components in the boiler room, one thing I noticed is that the copper pipe leading into the slab/flooring is not particularly warm to the touch (and the temp meter reports sub 100 F temperatures). In addition, the exhaust for the flue gases leaving the boiler is hot. To me it suggests a bad pump or a a clogged boiler. Not sure which one. Any ideas on how to determine if the pump is working or not? It does hum when its turned on - just don't know if it is pushing any water. I have to admit that these past 5 years I never paid attention to it. Infact I did not even know that the pump I had was one that needed oil every year for lubrication - so I never lubricated these past 5 years. Could it be that the pump is hosed? I did take off the cover on the coupling and saw the motor spinning, and the coupling does not rattle as if broken - not sure if the pump is working though. Could it be anything else? Any thoughts on how I should proceed are welcome. I am still learning the system. Any help is much appreciated.