I have a 4 year old PDC Bermuda spa that I bought a few weeks ago. I believe it is working ok, but I have a question about the heat recovery of this spa. It is a 325 gallon spa. When I filled it, the water started at 42 deg F. It took about 18 hours to heat up to 99 deg. F. This is just over 3 deg/hr. Does this seem about right? The heater is a 240 volt 4Kw heater. The cover was on the entire heating time and seems to be in good shape (once the spa was heated, there would be frost on the cover in the morning).

The other thing I am trying to figure out is how quickly the spa should recover while we are using it. The spa is at temp (99 deg. F.) when we get in, but once the heater kicks on (at 98 deg. F), it takes a long time like 45-60 min until the the heater shuts off at the setpoint (at 100 deg. F) if is shuts off at all. While this is somewhat in line with the original heating rate, it seems as though it's too slow. Sometimes the first heat cycle will work ok, but subsequent cycles never get the temp to the setpoint.

The only thing that I've checked electrically is to make sure that I have 240 Volts across the heater elements (I do).

My understanding is that elements either work or they don't. Can they get "weaker" and still work somewhat? I looked at the heater element itself and it seem to be in good shape. The is no scale or calcification. The color of the element is the same blue color as the plate that it mounts on.

Any help would be appreciated