There is a lot to your questions to answer and I will be brief. 1) VS501 has plugs for 2-speed pump 1, 1 speed pump 2 (that then uses the blower receptacle) and a circulation pump. When circulation pump is used, the setting to have pump1 function in both speeds, has to have both A5 and A9 dip switches ON. The circulation pump will then run continuously with 3 deg F setback. 2) BP501 as it comes from the factory comes only with a 5.5kW heater. To install a 4.0 kW unit it would have to be a field conversion. For example we can do it. Whether an E14 will work with M7 spa pack equipped with a 5.5 kW heater is a bit of a crap shoot. In principle it should if the flow resistance in the circulation circuit is low enough. For sure if the circulation system doesn't deploy 1-1/2" piping that would be a red flag. However when a 4 kW or 3 kW heater is substitute the flow requirements drop from 23 GPM to the kw ratio ( 4/5.5 or 3/5.5) and in that case I would not have much worry, if the piping is 1-1/2" which it should be with a E14. Balboa told me they tested the BP1500 (which has a 4.0 kW element) with the E14 and it worked fine. shareit vidmate app
