Gas heater needs 2750 RPM to fire

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I think you would be better off sticking with the current adjustable valve and just adding an actuator for automation for several reasons:

A) No plumbing changes
B) Fine adjustment of flow
C) No risk of adding too much head loss, with bypass check valves, while in spa jet mode making your jets weak
 
The problem with a manual valve is that you need to keep adjusting it and someone is eventually going to make a mistake and leave it open and cause the heater to fire without flow.

It is very important to understand that the heater does NOT have any sort of flow switch or any way to verify flow.

If the bypass is left open, the heater might get enough PRESSURE to close the PRESSURE SWITCH even though there is insufficient flow.

I would install a real FLOW SWITCH, so that the heater only fires when there is enough FLOW.

A spring check (2 psi to 7 psi) valve will automatically begin to open only when there is at least 40 gpm going through the heater, so it does not need to be adjusted.

You can just leave the bypass closed at all times as long as the flow does not exceed 100 gpm.

How many jets do you have?

How much flow does each jet need?

Are the jets too strong, too weak or about right?

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jmcmd1980 said:
The only problem, is my heat screen shows "Check Flow" at under 2750 RPM. If I put the pool in "Pool Heat" mode, the pump speed increases to 2250 at set, "Check Flow" still shows on the screen, the heater comes on line, but when the gas fires, it goes off after a few seconds. If I increase the RPM to 2750, the heater comes on, gas ignites, and pool heats to my set temperature.
Click to expand...
Seems like the heater does a pretty good job of detecting low flow on it's own. Plus I am sure it has a thermal limiter that protects from overheating. An extra flow switch seems unnecessary to me.
 
I know what it does but I don't think it changes anything.

In pool mode, no issues running at low rpm. The unit will turn off bypass when heating.

In spa mode, the head loss is higher and flow rates lower but that is only until spa heats up. After heat up, jets are at full strength.

When we use the spa, we don't get in and use the jets until it is heated anyway.
 

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You can install a VersaFlo.

We still need to know how much flow the jets require.

If the jets need less than 100GPM, then you probably don't need a bypass.

If you don't need more than 100 GPM, then just close the bypass and leave it closed.

If you need a bypass, then a manual one is a pain because you have to constantly keep messing with it and it is only a matter of time before someone sets it the wrong way and damages the heater.

If you need more than 100 GPM, then a spring bypass with a 3 to 5 pound (PSI) spring makes it simple..

1691950723826-png.522036


Bypass Valve Kit (# STK0135)

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AquaCal Bypass Valve Kit | STK0135

#AquaCal Bypass Valve Kit | STK0135
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1691886005843-png.521850



In any case, I would install a Flow Switch to make sure that the flow is good before the heater can fire.

Relying on a pressure switch to act like a flow switch is a bad idea.
 
mas985 said:
If it only 2 PSI that begs the question of why tripped initially. Perhaps it just needs some adjustment.
Click to expand...
The pressure switch comes set to 2 psi and the assumption is that there must be at least 40 gpm if there is 2 psi of pressure, but this is a flawed idea.

You can increase the pressure switch activation pressure, but that means that more flow is required to close the pressure switch.

In any case, the pressure switch can be closed with zero flow and cause the heater to run with no flow.

You don't want to rely on the high limit switches to turn off the heater.
 
That is why heaters have thermal limit switches. Low flow rate results in high temperatures which trips the thermal limit switches.

IMHO, flow switches are unnecessary when there are redundant thermal limiters.
 
mas985 said:
That is why heaters have thermal limit switches. Low flow rate results in high temperatures which trips the thermal limit switches.

IMHO, flow switches are unnecessary when there are redundant thermal limiters.
Click to expand...
I guess we will have to disagree on that.

The heater can be damaged by the time a high limit has time to trip.

In my opinion, manufacturers are foolish not to include a flow switch on their heaters.

They can include one for SWGs, so why is it such a big deal to put one on a heater?

It wouldn't even require a redesign, just install the flow switch and connect the wires that would have gone to the pressure switch.
 
The high limit switches are mounted on the header assembly, which is outside of the heat exchanger.

The heater transfers about 93 btu per second to the water, so if the heat exchanger holds 2 gallons of water, the water temperature increases by about 47 degrees per second.

If the water starts at 86 degrees, it will reach 212 degrees in 2.7 seconds.

That's not a lot of time before the heater hits boiling point and seriously damages the heater.

The high limits are also going to have some lag time before they heat up and trip.

If you close off all flow to your heater and fire it up, the heater will probably be seriously damaged.

The high limits will probably not trip in less than 2.7 seconds.

The water will boil and expand and this can cause the heater to explode.



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All is thermally connected with metal which has very low thermal resistance and very high thermal conductivity. There is very little temperature difference between the water, the heat exchanger and any other connected metal to the heat exchanger.
 

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