my 02 tub has suddenly burnd the heater element, its is a 4k balboa when I look to replace it Im told by spa people the 5.5 will fit and work just fine after buying the 5.5 and installing thinking alls well no heat. Back at square one testing the heater again I discover the new element is burned out. Spa people assure me the difference in wattage not a problem having an electrician check it find nothing out of order get yet anoyher 5.5 and install now comes the problem. The element holds and heats but seems to get too hot like it were dry fireing but knowing that not to be the case as I have flow from the low flow circulation pump but the element seems to be getting too hot as if there is no enough flow.so I turn on the main jets which works fine and the tub heats up to normal temp, Thinking alls well I leave it, upon checking it later I get OH code So I am coming to the conclusion and correct me if Im wrong the 5.5 is too much for this particular system or I have a voltage control problem. Any help will be appreciated.

5.5 KW is the norm for 220 volt ratings on elements.
Any and all elements will burn themselves out (dry fire) if not submersed.
There is a flow, or air source issue to cause an element to dry fire.
Your Grundfos pump may be clogged, on top of a faulty flow switch.
Your Two Port Return jet may be clogged.
Your Drain hose Bib may be allowing air into the suction side circuit.
The OH error points to a flow issue.
Perfect PH, Baqua Spa, Calciun Hardness increaser, Pinestraw, Clogged filter,
Debris such as Bromine lid check valve, or air bleed valve in the return, blockage
in main wetend feed 3/4 hose to Grundfos??

Pull one leg of the heater feed before installing another element, and address
flow issues.