I need to know if anyone who has a good experience on solar space heating would be willing to charge me for a consulting fee in order to guide me with interactive written instructions on how I could learn how to maximize the solar heat that I could store in a 200 gallons solar water tank when the outside temperature is very cold. I also would like to learn, realistically, what is the maximum stored solar water tank temperature I could get during cloudy and non-cloudy days when the ambient temperature feels in the low digits degrees Fahrenheit. (Note: A contractor already charged me for buying and installing six flat solar panels on a roof facing south; the heat is collected by those solar panels, then glycol circulates within those panels and that glycol is sent within a metallic tube into the 200 gallons water tank; the glycol then heats the water within the 200 gallons water tank).

 I would be more than happy to see my questions and answers posted in this forum with some people “chipping in” in order to also add good free opinions.

Start with telling us the following info:

1 your zip code or location

2. size of the panels  ex 4X8

3. angle the panels are mounted with respect to vertical

4. exact azimuth the panels are facing

5. model name and model number of the panels.

If you have paid a contractor to do something that does not work, I would certainly lean on him to make it right.

I once had a house with such a system and it was a PITA to keep running (which is should not be).  I am sure you have a circulating pump, temperature sensors on the collector and tank and a contol that lets you set the temperature differential between sensors to start and stop the pump.  There should also be an expansion tank.

The problem on my system was the system would easily air-lock despite having vents installed (I think the expansion tank was too small).  I'll guess your problem is either an air lock or a problem with the sensors or control.  There are not too many other things to go wrong.

As long as it was sunny, we could always get hot water (although the temperature outside of Barcelona rarely fell much below freezing :-)

You should have pressure gauges on the glycol loop and the water tank.   You probably also have a water supply that permits you to add water to and to pressurize the glycol loop.   The pressure in your tank (street pressure?) should always be higher than you glycol loop to prevent contamination in case of a glycol leak.

Bruce