Hayward H400FDN temperature sensor

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jerryk1234

Bronze Supporter
Jan 22, 2018
165
Hayward, CA
Hello!

I'm trying to solve an intermittent "SF" error code on my heater. OK, that's the temperature sensor. It mounts at the left hand edge of the manifold. No big deal, right?

The Hayward service manual lists it as P/N FDXLTER1930. They're all over Ebay & Amazon. OK, I bought one. Went out to install it this morning.
Why won't it screw in? Whups, the old one is DIFFERENT. First of all, it's all plastic. Second, it has an O-ring to seal it instead of goop or teflon tape.
Third, it's SMALLER DIAMETER than my new FDXLTER1930.

Clearly, the FDXLTER1930 is the wrong part for my heater. I websearched till my eyes bugged out, and found nothing else.

Anybody have a clue? The wife wants her pool back, sooner rather than later :). I guess I'll be calling Hayward tomorrow.
 
Can you show us pictures of the sensor you removed and the one you bought?
 
ajw22 said:
Can you show us pictures of the sensor you removed and the one you bought?
Click to expand...
After the new one comes in tomorrow. I paid as much for next-day shipping as the cost of the part. My wife wants her pool back!
The aftermarket folks haven't made these yet, so the only choice is genuine Hayward, and priced accordingly. Right now, the old
sensor is back in the manifold, so at least the pumps & filters can run.
 
OK, the new sensor came in, I installed it. I didn't bother to close valves - I just powered down the heater, unscrewed it, and screwed in the new one quickly. I figure a half gallon of water squirted out, no big deal.

UNFORTUNATELY, the heater still doesn't work. Same "SF" code. I tried cleaning the pins on the PC board connector with DeOxit and Q-tips, no joy.

I took the sensor to my garage lab ( I'm an electronics geek ). These sensors clearly consist of a pair of
identical temperature-sensitive resistors. Ohmmeter says they both work. About 12K ohms at room temperature. I compared it to the wrong sensor that I had bought from Amazon - resistances a bit different ( 15k ) but same pattern.

So it looks like I need a new Integrated Control Board. Luckily, these are available cheap on Amazon.
 
The sensors are 10K thermistors.

If you want to confirm the board is bad then connect two 10K resistors to the board. The temperature should read 76F.

If the heater still throws a SF code then it confirms the board is bad.

Every electronics geek should have some 10K resistors in his junk box.

Temperature Sensors - Further Reading

www.troublefreepool.com www.troublefreepool.com

10K_thermistor_chart.png
 
jerryk1234 said:
So it looks like I need a new Integrated Control Board. Luckily, these are available cheap on Amazon.
Click to expand...

Members have had mixed experiences with non-OEM heater PCBs. Be prepared to return it if it does not work 100%.
 
Well. The control board is going back to Amazon. I never took it out of its antistat bag. Why? Because the heater is leaking water. We've had a lot of rain lately, and it went unnoticed. Water is leaking - I guess out of the heat exchanger - and internal sheet metal has rusted out. I suspect that the heater is toast. This is the SECOND time this has happened. The first time, it was replaced under warranty, but that's gone now.

My understanding is that there are two popular leaks with these things - the plastic manifold can crack. Also,
the heat exchanger tubes can leak, possibly due to bad chemistry. Now, I keep reasonable track of my chemistry - it's a saltwater pool and it does trend alkaline. I could probably be more on top of that. I don't run excessive salt, and I have a sacrificial anode in the pipe.

A new heater costs $3600 on Amazon ( ouch! ). I should probably take it apart a bit and see exactly what's leaking. And also, what's rotted out. I popped open an access panel on the opposite side from the manifold,
and the sheet metal there is totally rusted. Gone.

If I'm going to pony up $3600 plus tax for a heater, maybe I should bite the bullet and just upgrade to a heat
pump? We have a relatively benign climate here in the SF Bay area, so it could work year round. HOWEVER, we also have some of the most expensive electricity in the country. It varies by time of day and time of year from a low of .36/kwh to an eye-popping 61 cents.

We have a solar heating system on the pool. During the spring, summer, and fall, we don't run the gas heater at all. It helps that we have a power cover, and the pool is always covered when we're not swimming. The power cover itself is an effective solar heat collector. The heater only comes on in the winter, and then we start seeing gas bills of $1000-$2000 a month.

I had PV solar installed on the house when we put in the pool, because I knew that without it, the electricity
bills would kill us. Right now, we're spending about $1K/year on excess electricity - that would be considerably
worse with a heat pump.
 
Hello - our Hayward H400FDN seems to have bit the big one. I'll be taking it apart to verify. I was thinking of going to a heat pump. Those pull a LOT of electricity. I was just looking at a 137K BTU one. It says "minimum circuit breaker 53A". That's a LOT of juice, over THIRTEEN KILOWATTS.

But I doubt that the unit draws that much as a steady state. It's probably starting surge.

Sigh. I probably don't enough juice out at the equipment pad to run this thing. That could trigger a major electrical
upgrade for the house. What with the pool stuff and the solar, our main breaker panel is maxed out. No place to put
anything else.

Might be able to get by with just a panel upgrade - to get more space, and not have to upgrade the actual service. Because
the current from the solar goes backwards, and doesn't count. You can put in a 400A panel and downgrade it to 200 by
changing out the main breaker.

Lessee - if this thing draws 8 kW and runs ten hours a day, that's 80 kw-hours a day, or $40 per day on average. Times 30 days in a month, that gets us to $1200/month. OK, that's a bit cheaper than gas, but definitely not free. I could put up
more PV solar to offset it, but that's a BIG investment.
 

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You did not indicate the volume of your pool.

Assuming a 30K gallon pool. 140K heat pump. Further assume 5dF (degrees F) demand daily (may be off, but just an assumption). You can change any assumptions and recalculate.

30,000 x 8.3 = 249,000lbs of water.
249,000 / 140,000 = 1.77 hours to raise temp 1dFF ( this will be optimistic for a heat pump, heat pump efficiency varies dramatically with the air temperature/humidity, only reaching the listed BTU number when the air is quite warm)...but let's roll with it.
1.77 * 5dF = 8.85hours of heating. Because of the optimism above, let's say 10hours
Heat pump Consumes about 5,000W/hour per 100,000 BTU. So 7,000W per hour for 140K unit.
10 hours, 7,000W, $.38/kWh = ~$35/5dF. (You can change $ to your rate)

So your calculations are roughly correct.

Gas heater
400,000 BTU * .8 efficiency =320K BTU
249,000 / 320,000 = .78 hours to raise 1dF
Gas heater consume 1g/h/100K BTU
Hourly consumption = 4g/h total
.78 *5dF = 3.9 hours
3.9 hours * 4g/H = 16g/day
16g/day = 19 Therms
Assume Gas is $2.5/therm (did a quick lookup in Hayward, CA).
19 x 2.5 = 47.5/Day

You can change to your rates/assumptions and re-calculate.
 
Edit the subject line of your first post if you want to change the topic from the temperature sensor to heat pump.
 
So. I find that I am confused. I took the top of the heater apart, getting me access to the heat exchanger. It doesn't look
happy. All covered with green copper oxide. But... I'm not sure - is it *leaking*? Or was stuff rusted out by rainwater? There is
rust ABOVE the level of the exchanger. Nah, that's wishful thinking...it's leaking.


20241218_115920.jpg20241218_115920.jpg20241218_115908.jpg20241218_115904.jpg20241218_115901.jpg20241218_115900.jpg20241218_115853.jpg
 
So: This heater is pretty much toast. Yeah, I can buy a new heat exchanger, but what about that rusted out sheet metal? The lower box doesn't even seem to be listed in the parts diagram. I suppose if I wanted to get creative,
I could do something with sheet metal and pop rivets....
I hesitate to go buy another H400FDN. They just don't last. What about the ASME version? It costs a grand more, but if it lasts longer, it might be worth it.
 
OTOH, if I buy a new heat exchanger for $1300, that's ALL the water stuff. It comes with a new manifold.
Maybe I should take the heat exchanger off entirely and see what's under it. The heater was working as recently
as a couple weeks ago, so I don't think the firebox is gone...
 
PoolStored said:
You did not indicate the volume of your pool.
Click to expand...

21500 gallons, according to Pool Math. 60x12, 3.5 feet deep at the ends, 4.5 foot deep at the middle. So
average 4 feet deep. It's a lap pool. Not for diving.

PoolStored said:
Assuming a 30K gallon pool. 140K heat pump. Further assume 5dF (degrees F) demand daily (may be off, but just an assumption). You can change any assumptions and recalculate.

30,000 x 8.3 = 249,000lbs of water.
249,000 / 140,000 = 1.77 hours to raise temp 1dFF ( this will be optimistic for a heat pump, heat pump efficiency varies dramatically with the air temperature/humidity, only reaching the listed BTU number when the air is quite warm)...but let's roll with it.
Click to expand...
*** And the "prime time" for running the heat pump - the afternoon - is also the "prime time" for electric rates.
61 cents per kilowatt-hour. KaCHING!

I am SO glad that we invested in a solar heating array and a power cover. On the other hand, thanks to that stuff, we don't run the heater for months on end. Maybe that's not good for it?

- Jerry
 
This morning's news trumpeted yet another rate increase for the local utility. That's SIX increases this year....

ANYWAY, my options seem to be:

* Fix the heater. I can buy a new heat exchanger for $1300. But what about that rotted sheet metal underneath? Replace it? Pop rivets?
In order to even look at that, I have to remove the heat exchanger. And to do that, I have to shut down the whole pump-filter system. Don't
want to leave that shut down for a long time. Make up a dummy heater bypass consisting of a piece of pipe and the matching quick-connections? I don't think that internal sheet metal is the actual firebox...

* Replace the heater. I'm reluctant to use the same model, which lasts a couple years. They have an ASME-certified version that's supposed to have thicker metal, and reasonably should have longer life. Costs about a grand more than the consumer version. Might or might not
be a direct drop-in.

* Replace the heater with something different. Raypak has heaters of a new alloy called "Nitek". They claim that it's
twice as corrosion resistant as cupro-nickel and has heat transfer properties as good as copper. The problem with that is
- the setup for the Raypak is totally different from the Hayward. So I'll be rebuilding the whole 2-inch PVC setup. Might be
beyond me, although I routinely do 1-inch PVC constructions for irrigation.
 
jerryk1234 said:
* Replace the heater with something different. Raypak has heaters of a new alloy called "Nitek". They claim that it's
twice as corrosion resistant as cupro-nickel and has heat transfer properties as good as copper. The problem with that is
- the setup for the Raypak is totally different from the Hayward. So I'll be rebuilding the whole 2-inch PVC setup. Might be
beyond me, although I routinely do 1-inch PVC constructions for irrigation.
Click to expand...

The Raypak Avia Nitek heater is new, and we have not heard about any members' experiences with it.

Nitek – Raypak

Raypak Pool & Spa, Residential and Commercial Hydronic Products -
www.raypak.com www.raypak.com
 
Yesterday, I had a visit from a pool repairman. This is a company that specializes in heaters. They are also a warranty service provider for Hayward.

He looked at my heater - which I had mostly taken apart - and agreed that it was toast. He said the damage was due to condensation. And *that* was due to 1 of 3 things:
* Inadequate ventilation - not an issue because it's mounted outdoors.
* Inadequate water flow - probably not the issue.
* Inadequate gas supply. Piping too small.
This last is what he thinks is the problem. Back at the house, there's a small-diameter pipe connecting the "house" stuff to the pool stuff.
Also - the earthquake valve is too small. If that's true, I have a bone to pick with my pool builder. If their inadequate installation causes
a 20-year heater to last only 2-3 years, I think they owe me a fix.

Does this sound reasonable?
 

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