Balboa BP7 shuts off with "Heater May be Dry" error (but only on Low speed) Balboa thinks this is because the pump is mounted 27" below hot tub

[chrispomeroy]

I installed a Balboa BP7 spa pack on my old 250-gallon hot tub which uses external plumbing.   I used it for a bit, then shut it down for 2 years as my vacation home went through renovations.  

The last thing I remembered I needed to fix was to swap the polarity of the pump, as High and Low were switched accidentally during the install.

 

This week I filled it and started it up. After a few minutes, it stops running and says "Heater may be dry" on the topside controller.

 

If I toggle the pump into high speed it will stay there without error (of course until it switches automatically to low after about 15 minutes, then it will error out 1 minute later)

 

SpaDepot.com helped me with some diagnostics, but they believe the reason I am getting this error is because my pump and spa plumbing are mounted 30" below the surface of the hot tub (in a "plumbing cabinet" below my deck). 

 

When I bought this home it had a Gecko Spa Pack, same pump, and ran fine.  

 

 

 

 

 

Is it possible the 27" of water "head" pressure is causing this issue?   Seems suspicious...

 

Should I just upgrade to a pump with higher flow rate? (BP7 manual says it needs 23 GPM minimum, but I have no idea how to measure this)

 

Can I get a higher flow rate simply by moving from 1HP to 1.5HP? Or by moving from 1.5"  to 2" PVC throughout?

 

Are there any other diagnostic tests I can try to see if the pump low speed is working?  By my hand, the low speed seems normal in terms of felt pressure from the jets.

 

 

 

 

 

 

 

Here is the setup:

• 250 gallon hot tub, external plumbing under the tub
• 240V Balboa BP7 with 5.5Kw 240V heater
• One 120V Pump - Two speeds (Sta-Rite)
• External filter housing
• Wifi Module I installed

 

Here are the diagnostic steps I have tried:

• blower jets (4) are all open
• Cracked open the bleeder valves on pump wet end, and filter housing, to vent air.
• Cracked open the unions before and after the heater, to vent air
• Removed filter from filter housing
• Ensured Gate valves are open 
• Restarted whole system (power off/on)
• Refilled hot tub again (I am now on the second fill)

[chrispomeroy]

Current setup. 

 

The "ceiling" you see in this pic is the deck surface the hot tub is sitting on.

[Spa Board Doctor]

It is possible that the four jets do not allow enough water flow across the heater in low speed.  If the jets have removeable internals, you should try to remove them, to see if allowing unrestricted water flow gets rid of the error.
 

[chrispomeroy]

That's interesting.  I might try that.  I don't know if I can unscrew the outer ring and remove the jet.  Probably can. 

The hot tub company I hired to look at it also agrees it's probably a flow issue.  They say it is not a guaranteed fix but they want to replace the heater temp sensors. 

I also bought a flow meter.  I haven't installed it yet but it might help provide a clue on flow rate on low speed.

[CanadianSpaTech]

Since Trumps Tariffs I am (Canadian) really having a hard time helping Americans but today I will make an exception only because what I see you may never.

It's how we all feel up here. Is what it is.

First

5 hours ago, chrispomeroy said:

They say it is not a guaranteed fix but they want to replace the heater temp sensors. 

No

Flow issue... Yes. 

Looking at your plumbing where it enters the face of the pump you have a Tee and a down pipe with a closed ball valve I can only assume is to drain the spa? 

So for the water to enter the pump it comes down the pipe hits the ball valve and goes back up and into the side of the Tee then into the pump face and pushed through the heater tube and the rest of the system back into the spa. 

Is there turbulence/cavitation occurring at the Tee junction adding air and/or reducing flow on low speed?

Might have used a WYE fitting here but a direct 90/45 would be preferred.

Research "liquid flow Through a Tee fitting". Perhaps you can find someone fluent in fluid dynamics. 

IMO everything else should be/looks correct... even the 30" lift

Is this the cause of your issue... no idea I'm just spit balling but as a last resort should be considered if all else fails.

@Spa Board Doctor thoughts on this?

Like @Spa Board Doctor said try removing jet internals and increasing flow.

Good Luck.

 

 

 

 

[Spa Board Doctor]

The "T" at the intake looks okay to me (providing no air leaks, as per CST).  Like my Canadian friend, I think it's a flow issue.  Use test mode to see it.

[chrispomeroy]

The spa tech company replaced the 2-3 year old heating sensors and fixed the issue. 

Am I 100% sure it was the sensors, perhaps just having the whole unit powered down for 2 hours could have helped clear out an error state?   I have no idea -  I was not there during the repair. 

All I know is for $200 I met a great spa tech I can use again and my hot tub works now reliably, so I won't argue and its a win win.

Some of the plumbing decisions are a little silly, for example it should probably use 2" pipe everywhere and use less street elbows so I may address that in the future.