Clanging noise sr400lp

[Ed Brinkis]

Good Afternoon all,

I have a 4-5 year old sta rite sr400lp heater. It has become recently problematic. When turned on, starts up normally, heats for a while, then a very loud metallic clanging noise occurs for about 4-5 minutes, the heater shuts down, waits for a while, then restarts. The clanging noise seems to be more frequent at higher temperatures. Eventually, it reaches the goal temperature but takes much longer than usual because of all the shut downs, not to mention the annoying clanging. If it helps, the clanging is never heard below 90 degrees or when the pool runs with the heater off, and is clearly metallic in nature. It is irregularly irregular -- think of a marble bouncing around and intermittently hitting a fan blade, rather than a rhythmic tapping / hitting. I have had a repairman come out and tell me that there is a "water impeller" in the sealed bottom unit for pumping water that is damaged, and the only solution is to change the entire heater. Being of a curious (and cynical) nature, I looked at the full schematics of the unit and fail to find such a "water impeller" anywhere in the diagram. While I am unfamiliar with pool equipment, I routinely repair all kinds of devices. It seems to me, whether right or wrong, that all water movement in the system comes from the main pump which pushes the water through the filter and the heater, with no separate pump unit in the heater. The fact that he quoted me a price more than double than the highest price I can find for the heater made me even more suspicious. I know I have the ability, knowledge and tools to safely and correctly swap out the heater itself, but I don't even know if it is necessary. I have found one such similar listing on another website, where the noise was not metallic in nature, but caused by steam clanging from a broken manifold bypass valve bypassing the boiler. Has anyone run across something like this or have any other ideas as to what might be causing the problem? I would love to swap out a module rather than coughing up the big bucks for a brand new heater. Any and all comments or suggestions, including diagnostic advice would be greatly appreciated. Thank you.

 

[ps0303]

You are correct about your assumption of that tech that came out. He has no clue what he is talking about. You are very correct in that it could be a broken bypass or just the thermal regulator. Since you have the schematics on the unit, you should see where the regulator is and it's very easy to remove. You can remove it and turn the unit on for a short time to see if the noise goes away. Now you may also have a broken bypass as well but it's easier to start with the regulator. A visual inspection might show you that the regulator is in bad shape. To test it for operation, remove the regulator, turn heater on, hold with with a pair of pliers over the exhaust and see if it opens as it gets heated. If it does not, change it out with a new one and see if the noise goes away. If the noise is still there, then the bypass is probably broken. You can replace that as well but lots more work.

 

[Ed Brinkis]

Thank you very much for your suggestion. I will try the thermal regulator first, as you suggest. I will order a new thermal regulator kit to have on hand when I take apart / test the old one, so if something just happens to break / tear, etc, at least I'll have what I need to fix it (I've been in that position before!). If the unit tests good and has no problems, I can always return the new kit and then try the manifold bypass. Either way, I'll let you know what happened. Thank you again!

 

[Pool Clown]

My money is on the manifold by-pass valve, not the thermal reg.

As stated, your tech is clueless, and should not be called back to replace the by-pass. You will need to remove the manifold to replace the by-pass. A bad thermal reg will trip the high-limit/AGS and just shut down the heater while the by-pass will cause the banging you are experiencing before the heater shuts down. You can remove the thermal reg to see if the by-pass is broken. A broken by-pass will usually make removal of the therm reg difficult (spring and thermostat will get hung up). While it is an extra cost, you may want to replace the therm reg at the same time depending on how old the heater is.
Thermal reg:
Kit: 77707-0010
just the thermostat (all you really need if replacing): 38000-0007S

By-pass: 77707-0001

 

[Ed Brinkis]

Thank you all! There were problems with both the thermal regulator and the manifold bypass valve. The thermal regulator was rusted shut and would not open even when heated with a torch, the manifold bypass valve was broken, with the valve and valve stem loose in the manifold. Both problems fixed, now back to being normal again. Thank you very much for all your advice!

P.S. Any suggestions on how to convince a Rat that the heater is not a good place to nest and call home (other than random heater use)?

 

[ps0303]

Pretty common for both to be bad in this unit.

You can try sprinkling some Bob Cat urine in and around the unit. I have some success with it. Do a google search for it and you will find it.