Should I put a WEAKER heater in my Great Lakes Ottawa Elite? (OH troubles)

[JSchmo]

So my spa has had an intermittent OH problem for a few seasons now, and I'm running out of ideas. The spa will run normally for a day, a week, a month, then go OH. Pressing any button restarts it and it may go a few hours, a day, another week, another month, then OH. Some times it will OH several days in a row, then not do it again for weeks.

Some pertinent details:

• Filter is new, and it doesn't matter even if the filter is removed completely
• All jets are open and functioning normally; flow seems normal
• Water inlets in bottom of tub are clean and clear of obstructions
• Slice valves are fully open
• Outside temp does not correlate with OH incidents; cold or warm, it does not seem to matter
• Temp is set at 98 currently and max temp recorded on an external sensor was 102, so it's possible the tub actually is going past its set temp. I have never seen it go anywhere near 118 or whatever the OH limit is, but it's hard to "catch" it right when it goes OH.
• New heater in 2013 (ThermProducts 5.5kW C2550-0408ET)
• New board in 2013 (Balboa 51421)
• New temp and hi-limit sensor last week
• Heater coil is centered in tube (verified last week)

Something I don't understand: if the actual water temperature in the tub is, say, 102, and if the tub display agrees and shows 102 (I have not verified this is the case, but bear with me), does the fact that the heater is (apparently) not shutting off mean the board is bad? A different way to ask that question: is the tub-wall temp sensor used for both the display and the board's thermostat? If so, the board must be bad, mustn't it?

Otherwise, I'm down to two ideas:

1. The flow isn't actually "normal" even though it appears to be; i.e. the pump motor or the pump itself is going bad
2. The heater coil is overpowered. This seems unlikely, since knowing how I approach these things I'm 99% sure I cross-referenced the original part when I bought the replacement. But who knows maybe the original unit was a 4kW and I shot myself in the foot with the new one.

So how do I troubleshoot from this point? I thought about maybe setting up a camera watching the panel display so I can see the temp change before it goes OH. And I suppose I should test the resistance of the (new) heater; maybe it's just bad?

Any other ideas are appreciated.

[Hottubprosne]

Possible bad motor. Does the tub have a pressure switch or is it m7? If the motor overheats and shuts of while the tub is heating the temp in the heater tube will climb over 110 and trip the high limit. Does the board have open contacts or the black sealed ones? Intermittent problems like this suck if you can get to a point where it goes oh everyday reset the tub once it is running and heating test at the heater should be 220. Then turn the temp down below the water temp so the heater shuts off then test and make sure the contacts released. Also run the pump on high for 3 or 4 cycles and make sure it doesn't shut off. Good luck

[Tman122]

How old is the pump? Do the jets have plenty of pressure?

[JSchmo]

Thanks for the replies.

Does the tub have a pressure switch or is it m7?

Well, the heater tube does have a pressure switch. Set to about 2 PSI if I'm reading it correctly.

Does the board have open contacts or the black sealed ones?

Sealed ones. The old board had open relays and I did actually find a sticking one, which is why I replaced the board.

reset the tub once it is running and heating test at the heater should be 220. Then turn the temp down below the water temp so the heater shuts off then test and make sure the contacts released

Good idea; I'll give that a try.

Also run the pump on high for 3 or 4 cycles and make sure it doesn't shut off

I'll do a specific test of this, but for what it's worth the tub never shuts off while in use (with pump on high).

How old is the pump? Do the jets have plenty of pressure?

As far as I know, the pump itself is original (so, 12 years old or so). I *think* I may have had the motor replaced several years ago, but it was not a DIY job so I don't have specific records. Maybe both parts are original.

The jets seem to be working normally. On low speed the "shoulder massage" jets on one seat are not just dribbling out - they seem to be squirting water the way I always remember. On high speed when we're in the tub it all seems pretty normal. But I've had this tub for over a decade and I've had the OH problem for at least 3 years so maybe it's degraded and I just haven't noticed.

So if I'm understanding both of you correctly, the modes of failure we're considering are:

1. Flow is low (due maybe to aging motor and/or pump) and hi-limit is being triggered during heating
2. Motor is overheating and stopping, causing zero flow and tripping the hi-limit
3. Stuck relay is causing heater to remain energized after heating cycle is over (perhaps during filter cycles)

Since the tub water is, apparently, actually getting over 98F I'm leaning towards #3, or some other board failure. If the tub is actually at 102, and the panel reads 102, the heater and pump clearly operated longer than the required time. If it was just the hi-limit, I would expect to have normal (or low) water temp in the tub. I'll try the tests and post the results.

Thanks again.