Raypak Heater Fires Up & Runs but Doesn't Heat Water

[Petebacher]

I have a pretty old Raypak R405B running on Propane. During this year's opening, I vacuumed last year's debris out the heat exchanger, checked and cleaned the burner, fired it up, then ran the heater for several hours but noticed no temp gain in the pool. It's a pretty simple pool-only setup with two valves plus the main filter valve - valves are all set properly and I'm getting good outflow on the return line and out of the over pressure valve when I crack it open. But the water that comes out is the same temp as the water in the pool (or just about!)!

Sure seems like the exchanger is getting bypassed (or mostly bypassed).

Anyway, I located a parts manual and found several parts that I'm sure are involved in my problem:
1) Bypass valve assembly
2) Unitherm Governor (looks like a car engine coolant thermostat to me)

Pretty sure at this point based on the diagram in the link below that my problem is the UG, so I've ordered one.

https://cdn.globalimageserver.com/FetchDocument.aspx?ID=F5FD17E4-A5DF-4E47-82BC-1A6A233FD9CF

Sound like I'm on the right track here?

Secondary question - shouldn't the heater be shutting down due to high temp in the exchanger? Could be one or more of the header sensors is bad? I'd rather have the darned thing shut down so I know it's not working properly, rather than heat the air in my back yard for several hours.

Finally, can anyone shed light on how I can ensure the bypass valve assembly is working as it should (and not allowing too much cold water to bypass the exchanger and flow back out into the pool)?

Thanks

-Pete

 

[Petebacher]

So I figured I would try removing the UG to see if that solved the problem (if the thing isn't opening properly, I should get hotter water with the UG removed).

Nope. Water is the same temperature. So I'm about to remove the header and see what the bypass assembly looks like...

Please chime in if you have any insight...

-Pete

 

[homegameroom]

I'm going to make a bunch of assumptions here....

The water coming out of my heater does not feel much better when the water going in is cold; I only feel a significantly noticeable difference when the water going in is relatively warm. I would never notice a difference in the temperature of my pool after only a few hours when the beginning water temp was 70 degrees.

Your heater safety systems are numerous; one of them should have shut the works down if the burners were on and nothing was getting heated. I assume the top of the heater is getting hot? Have you tried the same thing (heating the pool this time of year and/or had a noticeable difference in temperature after a relatively short time)in previous years with better results?

 

[ajw22]

Pete, if your heater is running then the BTUs are going into the water.

If there was too much cold water being bypassed and too little water flow through the heat exchanger then the water in the heat exchanger would boil. You would hear and see the heater shaking and clanging. That is a typical symptom of low water flow.

The coils in your heat exchanger could be rusted or clogged which would reduce the efficiency of the heat transfer. That is where I would go looking.

 

[JamesW]

You should get about 1.3 degrees per hour.

However, the pool can also lose heat.

If the heater had a problem, you would know it.

I suspect that it's working correctly.

Give it some time to heat up.

Get a good thermometer and wait at least 5 hours.

If it's cold and windy out, expect to lose some heat.

 

[Petebacher]

Thank you folks - I'm starting to think I may be overthinking it. The good news is I've learned significantly more about my heater than I'd known before.

So I removed both headers and all looks well - heat exchanger tubes are nice and thick with no significant scale, and the bypass valve assembly appears to be in good condition and moves freely.

My experience with thermostats is they do go bad, so I ordered one and will put it in when it arrives tomorrow - I'll save the old one just in case (and if I don't see a significant change in the outlet water temp).

Yes, I get that with significant water flow, you're not going to feel much temp gain, but it sure seems like an awful lot of heat is coming out the top of this thing and heating my back yard, especially compared to the temp of our house heater, which vents through a PVC pipe and is cool when it exits. Hopefully my next heater will be a bit more efficient. That said, I remember the water being nice and warm late last summer when the pool temp was up in the high 80s, so let's see how it feels once the temp comes up a bit.

Thanks for reading -

-Pete

 

[JamesW]

The heater is probably about 82% efficient. So, a lot of heat is lost to exhaust compared to the house heater, which is probably better than 95% efficient.

 

[Soupy]

Also, a pool heater can easily be 10 times the BTU output of a home furnace. It takes a lot of energy to heat 30000 gallons of water.