Sta-Rite SR400NA won't keep temp

[danix]

Kind of a weird one. I've done a lot of research and also gone completely through the troubleshooting guide.
Our heater had been working fine, then suddenly stopped keeping the spa at temp. We'd set it to 102, then it would end up dropping and getting cold, with the unit refusing to fire.
Then it stopped firing altogether. No warning lights on the back of the panel. Sensors seem to all be reading correctly.

• I checked for mouse/rat blockage or chewing, nope.
• I checked voltages, all good.
• I replaced the thermal regulator, no difference. Still would not fire.
• Called warranty company and pool contractor came out. Told him I thought it was the igniter or igniter module. He agreed.
• He confirmed unit not firing, replaced the igniter module. No difference.
• He replaced the igniter, said it wasn't reading proper ohms. Unit would not fire with the new igniter, so he thought perhaps someone at the office had put a used part back in the new box.
• Next tech came out, unit fired up right away to both our surprise. He said well it's working, let's try it and see.
• That night we ran the spa and it was fine.
• Next day, it got to temp, but again would not maintain temp.

I've left a message for the company to come back out but I'm kind of stumped here. Any thoughts?

 

[ajw22]

You may have an intermittent flame sensing problem caused by corrosion on the grounds. Next time it does not start look at the LED on the Fenwal box and see how it is flashing. Read Heater Flame Sensing - Further Reading

 

[danix]

I will look for the LED but there's zero corrosion on the grounds.

 

[danix]

Thanks. I checked the LED - 3 flashes, ignition lockout. Also cleaned all the grounds, no difference.

 

[ajw22]

Thanks. I checked the LED - 3 flashes, ignition lockout. Also cleaned all the grounds, no difference.

Three flashes indicates no flame current being sensed and ignition locked out

You have a flame sense problem. The wiki - Heater Flame Sensing - Further Reading takes you through testing the flame sense circuit if you have a true RMS multimeter and possible fixes for ground problems, running an alternate ground, and finding ground interference.

 

[danix]

Helpful link thanks. I do have a true RMS meter and checked the voltages. You can see what it's doing here
As far as I can tell, there's no ground problem, the voltages are doing what they should. At this point, there's no ignition again, at all. Tried at different outdoor temps from 30-60 deg, no difference.

Pool repair company is coming on Tuesday to test the gas pressure. They are telling me the size of the pipe is not what Pentair specifies, but I pointed out that it's been working fine for 3+ years even when I heat the whole pool, so I don't buy it.
They have to do all their due diligence for the home warranty company, until eventually I should get a new heater approved.

 

[JamesW]

It might be a gas pressure issue,

What is the line size and length?

 

[danix]

1.5" pipe comes off the meter and runs around 75-100 to the backyard. From where it exits, it's reduced to 3/4" and goes up, around and down to the heater, maybe about 20'.
I could see insufficient gas pressure impacting the ability to keep the temperature, but unless there is zero gas pressure, it doesn't explain the current lack of ignition.
Again, I've been at this house for 3+ years, hasn't been a problem until now.

 

[JamesW]

Let's see what the gas pressure does and go from there.

 

[setsailsoon]

Dan,
These types of problems can be infuriating. Couple of questions:

• Can you please check the gas supply line all the way back to the meter. We've had symptoms like this caused by a valve that was inadvertently closed by somebody or there was water trapped in the line or a corroded line underground that finally gave way. All were working fine for several years like yours.
• Do you smell gas anywhere?
• I hear a click and then see a change in voltage on the meter twice. Is the gas valve opening? Doesn't sound like the normal loud gas valve click to me. You may want to jump the gas valve with 24 vac momentarily to see if it's really opening. Do this with the unit off of course. Could also be a bad connection at the relay or a bad relay. If the valve is opening normally there should be a gas smell at this time if you don't have a flame. If you don't smell gas at this point out the exhaust don't go further. You have a gas supply issue that needs to be corrected.
• Are the red 3m connectors on the yellow ground wires part of the new heater installation or a repair? Doesn't look like they are properly installed to me.

Also, FYI corroded connectors are not going to look corroded. You have to check them by wiggling or cleaning. I've had them look "clean" and found just wiggling a wire or sensor made the unit fire up.

I hope this helps.

Chris

 

[Pool Clown]

Hold on guys, A flame sensing problem would only occur the first 3-10 seconds AFTER the heater fires, it would not keep the heater from initially firing. Pipe size? Maybe, but, i don't think it would allow the heater to fire for, say and hour, then decide the size was too small and not fire anymore. And if it were broken or full of water, i dont think you would get the intermittent operation.

If you are hearing the click of the gas valve, the system is working, and you have either some sort of gas delivery issue, or the gas valve itself. To confirm, I would put my meter on the wires to the gas valve (remove wires at the gas valve and connect meter to those wires). If you have voltage, re connect then check for gas flow through the valve. Easiest way to do that is if you can smell raw gas out through the exhaust during a call for heat AFTER pre-purge. If no voltage at all, its a control problem, board or Fenwal.

 

[danix]

Thanks for all the input, very helpful forum!
All valves are open and the earthquake valve is not tripped.
I didn’t speak to the tech as I was at work but my son said that he came out and said “tell your dad he was right” and had to order more parts.
I am guessing he’s confirming that it is not a gas pressure problem. Definitely no smell of gas.
if that gas valve is electrically controlled, that could be it. I did ask the first tech early on about it, asking if it was like a regulator.

I will try to get an update tomorrow.

 

[danix]

Just realized I never updated the thread, sorry.
Guys came out, I wasn't here but they said they replaced "a valve".
No signs of external changes on the gas plumbing, so I'm guessing it's something inside the unit itself.
Now when I turn it on, there's an obvious hissing kind of noise which in hindsight was absent before.
You can smell the gas right before it ignites with a big WHOOMP.
It's been good for a couple of weeks now.

Thanks for all the input, I learned a lot!

 

[setsailsoon]

Just realized I never updated the thread, sorry.
Guys came out, I wasn't here but they said they replaced "a valve".
No signs of external changes on the gas plumbing, so I'm guessing it's something inside the unit itself.
Now when I turn it on, there's an obvious hissing kind of noise which in hindsight was absent before.
You can smell the gas right before it ignites with a big WHOOMP.
It's been good for a couple of weeks now.

Thanks for all the input, I learned a lot!

Thanks much for the follow up. This isn't always given and it's very helpful to know. Can you tell us how much the repair cost? Sounds like the gas regulator itself which includes a solenoid operated valve. This would also explain the observation about not having the loud click and the comments @Pool Clown made.

Due to the safety risk gas regulators are usually manufactured to close tolerances and don't fail too often. A failure of the solenoid to open fully (weak coil) or partially plugged screen inside the valve could have resulted in this.

 

[danix]

The repair was covered by home warranty, so my cost was only $75 deductible and another $30 for the thermal regulator I had already replaced on my own.
vendor says in addition to the earlier work (igniter, igniter module) he said they also replaced the "gas valve inside the heater" and the "bypass regulator valve inside the heater."

 

[danix]

So... less than a month later, I noticed that the heater is taking a LONG time to get up to temp. I mean, it used to be 45 mins or so to get the spa up to temp, and now it seems to take 3+ hours.
For at least a week or so it was good, now it's like they installed the wrong size nozzle or something.
I will clean my filters just in case but the pressure is fine on the gauge and flow to the spa is the same as always so it's not obstructed.

I'm also pretty sure I smell gas and/or an acrid smell when the heater is running. I'm going to reopen my service request.

Also, warranty companies suck, though they may occasionally save money.

 

[Pool Clown]

Babysit the heater and see if it is cycling. It may not begin to cycle right away but rather once the water temp reaches a certain temp range. Make note of the temp at which it starts. if it starts at the mid to high 80's, then its probably the therm by-pass. Yes, I noted that you bought one. Was it a factory Pentair/Sta-rite part?

 

[ajw22]

If the heater is running then the heat has to be going someplace. The heater puts out a fixed amount of BTUs. The heat either goes into the water or the heater exhaust will overheat and the safety switches will shut it down. Check if the heater is shutting down and restarting after it cools down.

 

[danix]

Pool contractor asked me to make sure it wasn't the filter. To make sure, I cleaned the filter.
Spa starts at 59 deg (verified with laser temp).
I started the unit, and thought to point the laser at the exhaust vent. Normally, within a min or two, the unit fires with a loud WHOMP and literally vibrates the structure next to the equipment.
Right now, there's no WHOMP, just clicking of a relay, some indication of heat. Exhaust temp rises up to 104-105 then drops again, I let it repeat a couple of cycles then turned it off.
I again noticed what seems like an acrid smell from the exhaust. Normally you can sit there and roast hot dogs on the vent, now there's not enough heat and the smell burns your nose.
I reopened the case, let's see what they find. I realized today I've been dealing with this issue since Dec 5th.

@Pool Clown yes the thermal bypass was replaced with a factory part.

 

[danix]

Interesting that I chose the word "acrid". Did a search and the manual says this:

Symptom: Flame is “fluttery .” Exhaust may have acrid smell or burner may fail to stay lit.
Cause: Flame is too lean.
Remedy:
See page 16 and verify that the gas regulator setting is –0.2" (–0.5cm) wc.
Contact a qualified technician or service agency to replace the gas orifice.

Page 15 (not 16) of the manual talks about the gas regulator:
This appliance is equipped with an unconventional gas control valve that is factory set with a manifold pressure of –.2" (–0.5cm) wc. Installation or service must be performed by a qualified installer, service agency, or the gas supplier. If this control valve is replaced, it must be replaced with an identical control.