Gas fired steam boiler with a hot water boiler mate (aka...sidecar, boiler mate, heat exchanger, etc.. ) The industrious previous owner of the house installed a traditional hot water heater and re piped the boilermate to provide supply for a hot water loop in the basement of the house. System is piped as follows:

1. Circ pump
2. Boiler mate
3. P-X expansion tank (mounted with air valve up)
4. Taco 216 Swetchek with arrow pointing with flow (I don't know what is fitting does)
5. T connect with pressure valve (range 0 to +30psi) and Float Air Vent max psi 45
6. T connect with freshwater supply with Watts N450f (reducer set 12-15lbs, relief set at 30lbs) and Watts 156f feed.

Only other features after the last T connect it the pipe loop and baseboard units. The loop then completes back to circ pump.

Fairly regularly (once per week) I notice no heat in loop. I check the water level in main boiler to make sure it is high enough to fill boiler mate. Then add water to hot water loop system, typically until psi = 15. There are no signs of any leaks and I have been adding water like this for 3 heating seasons. Where does the water go? After reading other posts on your site I am curious if the expansion tank needs some type of adjustment? Is there other service that this loop should have? Thank you for any help you can provide.