CanadianSpaTech

The Balboa M7 technology has the sensors in the heater tubs so you won't need the old sensors. You might need a block out plate for the topside if the new one is smaller than the original. https://www.spadepot.com/eco-spa-Topside-Adapter-Plate-P3128 Also for spa pack here: https://www.spadepot.com/Balboa-VS-Spa-Control-Kit-P3185

Need better pics of the area with the 2 copper tabs and the 2 black squares above them. The copper tabs look all bent but hard to see what's going on. Do you have a multi meter and know have to safely use it?

Sounds like it could be a stuck heater relay. Disconnect the heater from the circuit board for testing. If left connected you could do some damage or even fire. It will boil the water in the heater tube in seconds. Post photos of the circuit board and the schematic on the inside cover so we know what you have. The flow switch should not allow the heater to stay engaged when the circ pump stops. The flow switch protects the heater. Test for 240V at the heater connections at the circuit board when the spa should not be heating and the flow switch is open. If it is still getting 240V look to the heater relays.

Disconnect the 2 copper tabs from the heater element and then test for 240V when the spa is calling for heat. If you get 240 replace the heater element if you only get 120V then you might have a bad/burnt relay. Remove board and look on back for darkened or burnt areas. Post pics of the circuit board and the schematic on the inside cover. Any Error codes? Is the spa in "Standard Mode"?

Remove it until you can get this figured out... again remove it from the equation. Ok to run without filter while testing for a day.

@RDspaguyI think there was a spam post that has been deleted. @Cusser post pics...lol 😄

Disconnect the blower and see if it heats up to set temp. Take it out of the equation. Make sure the temp probe is all the way in place. If the probe goes through the side wall of the spa and physically touches the water then it is all the way in. If the probe goes inside a tube and doesn't actually touch the water make sure it is pushed all the way in so it touches the front of the tube so it can read the water temp. If it's not all the way in it won't read water temp correctly. It should also have a plug or cover of some sort once it is all the way in so cold air does nor reach the back of the probe.

The top lid looks to be made by Waterway so I would suggest the weir housing is also made by them but likely proprietary to the MFG

I normally remove the sensor in the side closest to the element to make it easier to get it in/out. Also there are small o-rings just make sure they don't fall off when installing.

All we ask is pay it forward

https://www.poolandhottubdepot.com/balboa-4-0-kw-heater-element/ When you install it make sure the element is not touching the sides of the tube. Lots of youtube vids out there I'm sure. You should have a local store that will have them in stock.

pop the wet end off again and post photos of your shaft and we'll let you know how to proceed.... No @RDspaguy not you

See below. Do you have a multi meter and knowledge of how to safely use it? Lift the copper tabs up so they don't touch anything and try the power. If the breaker holds when the spa heat indicator light is solid and not flickering test the copper tabs for power. If you get 120V replace heater element.

That's a pretty large flash but hey you might get lucky. Let us know results.

Yes but look on the back of the board to confirm the relay is burnt and the flash mark is not from a previous repair. There is a flash mark so it should be noticeable. Test heater for continuity using multi meter. Test the 2 screws for 240V coming off the board when the spa is calling for heat. I suspect heater is still good. Then how did they test the heater? They would have to remove and reattach the wires to test the heater. It looks like the spade connector on the black wire is metal and different than the other spade connectors and possibly replaced at some point. ??? I would 100% get a small space heater inside the cabinet ASAP! There could be one way check valves in the plumbing system and you might get anti freeze to one side of it but not the other if it is closed. Waterfalls are hard to get the water out of as well. If they did not blow out the lines and suck out each jet there will still be water that could freeze and then you are in for huge repairs.

In the future please start your own thread/post please. https://www.manualslib.com/manual/598702/Balboa-Instruments-Ml551.html

If you live is sub zero climate get a small thermostatically controlled space heater inside the cabinet ASAP.

The heater is likely fine and just the relay is blown. You can test the heater white a black wires for continuity to confirm the heater is good. Well you can try de-soldering the old one off first before ordering (if you can find) a new relay. If you can get the old one off you are well on your way. I'm 25 years in and I still send mine out to a professional.

To test you can use a multi meter and check for 240V coming off the circuit board when the spa is calling for heat at the 2 screws below the blk and white wires. Disconnect the white wire from the board before testing. If you get 240 v you can use the 2 screws for your heater blk and white wire connection. If you don't see below. Looking at the last photo I can see a burn flash on the main housing behind the circuit board. The square black heater relay has likely blown and the tab breaking off is a by-product of that failure. The relay can be replaced much cheaper than replacing the circuit board. It can be done DIY but you need a bit of skill at soldering and can find the relay along with the correct tools for the job. Remove the circuit board and look on the back for the burnt area to confirm and the flash mark is not from a previous failure. Yes you could move that connector down to the screw below. I take my boards to a local electronics repair guy. Where are you located?

What is the water temp?

PR is not an error. It is a Priming Mode and the spa on start up will display PR for about 5 mins then the heater and filter cycle will kick in. You can bypass PR by pressing temp up/down once. If the water is cold (below 60 degrees) the spa will run the pumps until the spa gets some heat in it. You can turn them off and they will start right back up to prevent freezing until the sensors detects warmer water temps then it will run normal.

Are you sure it's not in a "Mode" setting like Economy mode. In economy mode it will only turn the heater on during the filter cycle and if you have a 2 hour filter cycle set for each 12 hour period it would likely only get to 85 and stop heating when the filter cycle ends.

no idea

Has the suction increased in the foot well pump return/suction covers when the spa is running in low speed? It is possible there is a one way check valve that has broken or stuck open. When the spa is running in low speed the water gets sucked in through the filters and the check valve remains closed. When the spa is put into high speed the check valve opens and pulls the extra water needed to feed the pump gets pulled through both the filter AND the footwell. If it has broken or is stuck open then it won't pull very hard through the filter. This is one possibility and only accounts for the low suction but not for heating slowly. Some spas have them.. some don't. Does the spa heat and filter using pump 1 or is there a circulation pump? Do you get any error codes on the topside? Post photos of the circuit board and the schematic on the inside cover so we know what you have.

3 dots flashing is a flow error. Remove filters and reset the breaker and run without the filter and see if it heats. If you still have issue after that let us know.