Hot tub heater troubleshooting issue

[Rig84]

No, because the moving water absorbs what little heat is generated. The housing won't feel warmer than the water.

Ok, so you think it's actually working, and it's just the lack of insulation that is causing it to not heat?

 

[LarryFine]

Ok, so you think it's actually working, and it's just the lack of insulation that is causing it to not heat?

Yes, a convertible hot tub heats very slowly on 120v. Yes, it must be covered for the heat to build up.

If you're really in a hurry, run a temporary 240v line to it. Or, partially drain it and fill with hot water.

 

[tom baker]

When I fill my hot tub I use 100 deg F water.
I have a tankless gas htr so endless hot water.

 

[Little Bill]

I disagree with the statement that the pipe wouldn't feel warm on the discharge end. It might not feel hot but you should certainly feel a difference between the feed end and discharge end.

 

[Little Bill]

@Rig84
By the time you charge for your troubleshooting time, you could probably get another heater and try it.

 

[Rig84]

Well guys, I'm about to leave the shop for the day and am going to stop by and check on this again. I'll make sure the jets are all closed, and tell him to get some kind of cover on it and hope for the best. If not, I'll try what "LarryFine" suggested and run a temp 240 line to see if that works. THANK YOU EVERYONE for the help!

 

[Little Bill]

Well guys, I'm about to leave the shop for the day and am going to stop by and check on this again. I'll make sure the jets are all closed, and tell him to get some kind of cover on it and hope for the best. If not, I'll try what "LarryFine" suggested and run a temp 240 line to see if that works. THANK YOU EVERYONE for the help!

See post #25

 

[Rig84]

Unfortunately this is a freebie job for a friend, or I totally agree with you, I’d just get a new one.

 

[Dennis Alwon]

No, because the moving water absorbs what little heat is generated. The housing won't feel warmer than the water.

The pipe coming out of the heater should be warm

 

[Jraef]

If it is pulling current, it is heating up. The problem is, how much?

Immersion water heaters work based on the surface temperature of the heater element making contact with the water. The actual surface temperature of the heating element can be expressed as "heat density" in watts/square inch. That heating element was designed for 6kW, so let's imagine it has 20 sq. inches of surface area in contact with the water, the watt density is then 300W/sq. in. When you connect it at 120V, it is now only 75W/sq. in., so the heat being put into the water is extremely low. It's entirely possible that you cannot discern the difference between the cold water coming in and the slightly less cold water going out. Factor that into the rate of convection losses in the tub walls and surface of the water, and it likely cannot keep up. That's why the cover will HELP, but even then, it might not be enough, depending on the ambient temperatures and the amount of insulation on the walls of the tub.

 

[kwired]

I disagree with the statement that the pipe wouldn't feel warm on the discharge end. It might not feel hot but you should certainly feel a difference between the feed end and discharge end.

The water is moving through fast enough that there isn't enough heat rise in the water that you can feel it. To begin with it would have to raise the temp to near or above your body temp before it even starts to feel warm, so even if there is a 5 or 10 degree difference across the heater if it is going from 60 to 70 you may not really be able to tell with your hand, but I think the water is likely moving fast enough you won't see that kind if rise in temp across the heater. Might even need very precise thermometer to measure any rise in temp.

I used to have a ~1500 watt @120 volt spa, wasn't a huge spa, maybe could hold 4 average adults but would be somewhat crowded and maybe only held 250 or 300 gallons of water. When first turning on after a fresh fill up (my well water probably only about 55F) you could plan on letting it run at least 24 hours before it will be near operating temp. Not having a cover doesn't help if air temp is cold.

Remember this thing is pumping same volume of water through the heater as it does when connected to 240 volts and is drawing 6000 watts, so it is going to be even colder temp coming out of the heater than it would be at 6000 watts, though I doubt it will be that easy to feel temp change on cold tub even at 6000 W.

 

[kwired]

Well guys, I'm about to leave the shop for the day and am going to stop by and check on this again. I'll make sure the jets are all closed, and tell him to get some kind of cover on it and hope for the best. If not, I'll try what "LarryFine" suggested and run a temp 240 line to see if that works. THANK YOU EVERYONE for the help!

Depending on design of the tub, jets may be where heated water enters tub. Simple tub like I had only had two inlets to pumping system and then the jets on other side of pump. That unit did run pump on low speed during heating so there wasn't very much air introduced while heating, when you wanted to use the tub it put the pump motor into high speed.

Believe it or not just running the jets at the high speed will add heat to the water from friction of water moving through the system. Won't heat as fast as the heating element though but when outdoor temp is fairly moderate will help maintain temp somewhat. Had an industrial process tank that held a pretty thick oil that wouldn't pump at room temp. Tank had a heating/cooling jacket in the walls and we had only a 15-20 gallon surge tank and pump as the method of heating that oil. Most the time just run the pump and friction of water moving through the system was enough to maintain temp, but if they wanted to speed it up they would add some steam or hot water to the surge tank.

 

[kwired]

This particular heater doesn't have a flow switch, at least not that I can tell. But the circuit board is calling for heat and the relays are operating properly and the voltage and current are both present at the heater wires. So even if it did have a float switch, it would seem to be working. Otherwise, I don't think it would call for heat, but I'm not too sure. This one really has me stumped.

Some have a pressure switch to prove pump is running.

I've seen some with temp sensor on input and output of heater - a differential here may be a way to prove water is flowing through the heater even if pretty small differential.

 

[kwired]

If it isn't too large of a tub this low wattage heater will maintain operating temps even in winter weather, presuming you do have it insulated and covers on. Mine did, it will take hours to see an initial warmup of 10 degrees though.

 

[ptonsparky]

How much limestone is in the heat exchange?

 

[kwired]

How much limestone is in the heat exchange?

Guessing if very significant element would have overheated and failed.

Don't think it builds up in same manner as it would in a storage tank water heater either, especially with the flow rate that is typical.

 

[hillbilly1]

Probably easily checked with an infrared thermometer. The body of the heater should show a couple degrees of difference from the inlet side piping.

 

[kwired]

If I did research and figuring correctly it should take an hour @ 1500 watts to raise about 621 gallons of water by one deg F. This assumes no losses, real world there will be some losses even with the cover on.

If your tub holds 621 gallons of water then it would take 40 hours to raise it 40 degrees (say from 60 F to 100F)

Pass that water through the heater at 5 GPM and you are not adding all that much heat to the water as it is passing through

6000 watt heater will heat 2484 gallons by one deg F in one hour. four times rate, of course because you are applying four times the energy.

Again if tub is 621 gallons then one tenth the time would be only 10 hours to raise it 40F. Considering pump probably moves maybe at least 5 GPM through the heater, I don't think you will have enough temp rise across the heater to be able to feel the difference even at 6000 watts and if you measured it would probably be less than a degree F.

 

[James L]

I think there's zero possibility that a 1500 watt heater will warm water flowing through a hot tub. Zero chance the pipe will be more than 1/2 degree different temp on the output.

Look at a tankless water heater, or any other "on-the-flow" heater. They are not rated to heat water up to a particular temperature, they are rated to perform a certain amount of temperature rise.

I installed a 10kw instant water heater, and it was rated to have a 50 degree rise with a flow rate of only about 2 gallons per minute. You cut the KW rating by 85% and increase the flow rate by 400% and I don't think it's mathematically possible to see any temperature rise

 

[James L]

If I did research and figuring correctly it should take an hour @ 1500 watts to raise about 621 gallons of water by one deg F. This assumes no losses, real world there will be some losses even with the cover on.

If your tub holds 621 gallons of water then it would take 40 hours to raise it 40 degrees (say from 60 F to 100F)

Pass that water through the heater at 5 GPM and you are not adding all that much heat to the water as it is passing through

6000 watt heater will heat 2484 gallons by one deg F in one hour. four times rate, of course because you are applying four times the energy.

Again if tub is 621 gallons then one tenth the time would be only 10 hours to raise it 40F. Considering pump probably moves maybe at least 5 GPM through the heater, I don't think you will have enough temp rise across the heater to be able to feel the difference even at 6000 watts and if you measured it would probably be less than a degree F.

I think I was typing as you were pressing "enter"

I didn't do any research, just kind of shooting from the hip. I agree 100%