Over the summer, I had a TT Solo 110 boiler installed in my home. The boiler uses propane for fuel and replaces an old oil boiler. My home has (3) zones of fin tube baseboard and DHW is produced using an indirect Amtrol BoilerMate. All zones use Grundfos 15-58 circulators on the LO setting. I've attached a photo showing the piping arrangement.
It is very similar to this arrangement except that the TT110 provides a seperate supply for the indirect DHW tank.
The installation was completed in August and everything seemed well with DHW production only. When we started using the heat in October, I noticed 2 issues.
1. The temperature of the DHW tanks drops when the heat zones are running. When the heat is not running, the tank loses 1 or 2 degrees per hour if no DHW is being used. When the heat is running, it can loses 10 degrees in 30 minutes. I've felt the supply and return pipes to the DHW tank while the heat is running and found that they do get warm. I believe that although the DHW circulator is not running, flow is being induced by the heat zones which is cooling the tank.
2. When a single zone of heat is running, the return temperature is within 2 degrees of the supply temperature. This causes the boiler to short cycle. I believe the problem is the flowrate through the zone is much lower than the flowrate through the secondary loop through the boiler. This causes supply water from the boiler to mix with the return at the closely spaced tees. The situation improves when more than 1 zone is running.
My installer recognizes the problem and is willing to make changes to solve the issues. Does anyone have suggestions for correcting these issues?