Raypak M206A Heater rattle or knocking noise

[hanesian]

My Raypak (model # P-M206A-MN-C) heater has two (perhaps related) issues that I would appreciate troubleshooting help with.

First, it is making periodic but regular noise, somehwere between a rattle and a knock. Here is a link to a video demonstration:

https://youtu.be/oV4NBzlaNCs

From reading other posts referencing a knocking sound, I understand a likely culprit might be a broken bypass valve, as TFP member Paul (ps0303) posted a helpful video about. Before attempting this repair, I wanted to upload a video of my exact noise to verify that this sounds like a broken bypass valve, as opposed to something else.

Second - and perhaps related - is the heater also seems to be inconsistent in staying on long enough to heat the water to the desired temperature. It kicks in and runs for a while, but then seems to prematurely shut down shortly thereafter so it is taking days just to get the water temperature up to the low 70's. I've backwashed a couple times to verify the water flow is good, and there are no physical heater bypass valves between the filter and the heater.

Any ideas on what could be causing this? A teperature sensor perhaps? Could this temperature issue be either a consequence of the above rattling noise, or perhaps related to it?

Thanks in advance for any helpful feedback.

 

[ps0303]

It is a water flow issue. So either you need to clean the filter or you have a bad bypass where it is broken and stuck in a way preventing proper water flow.

I had a similar issue on an inground spa and what was to be a bad internal bypass but when I opened it up there was the finish material from the spa blocking the flow of water. Cleaned it all out and the unit ran just fine. Owner has no clue why that was happening as he had not had the spa refinished in many years.

So check to make sure you have good water flow first and then then check on the internal bypass of the heater. MY video is of a Hayward and yours is a Raypak/Rheem so a little bit different.

 

[hanesian]

Thanks for your quick response.

I assume it is a bad bypass, as I've backwashed the filter several times and the pump pressure reading is normal.

I have opened up the side cover and unscrewed the unions to the input and output valves and can see the bypass valve and spring. The spring is rusty but I am not sure how to test to see if the valve is stuck, as everything I've found says to test it but does not clarify HOW.

How do you test to see if the bypass valve is stuck or not?

I can move the rusty spring itself from the right hand side, but cannot make the plastic part itself on the left move. Is the plastic part is supposed to move, and this means it is stuck and needs to be replaced?

TIA.

 

[hanesian]

Anyone know how to test to determine if an internal bypass valve is stuck or not?

 

[Pool Clown]

First off, I don't like to see flex piping used on this type of heater. There have been cases where the walls of the flex pipe separates internally causing a restriction and in turn slowing down the water flow through the heater. Even though the risers are ridged, they appear to have been subject to an over temp condition. They seem, from what i can see in the video, to have a little deflection (bending) in them.

What you are hearing is water beginning to boil in the heater and will eventually shut down the heater due to an "over temp" condition (high limit shutting the heater down). Heater shuts off, water running through then cools the sensor, it resets, and then the heater fires, and it starts all over again.

* Could be a bad thermal bypass (Raypak calls it a unitherm governor), or a bad / failing mechanical or (simply called) by-pass valve compounded by the "separating wall" plumbing restriction. Maybe the plumbing is in good shape, all i am saying is, is that
that type of plumbing is a candidate for that problem.

* You may have a chemistry problem, that is causing a heat transfer issue.

There are a couple of things you can check:

Take the unitherm governor out and see if it will open in a glass of hot water. My guess is that it will, but how far will it open? That's the tricky part. That part is supposed to open enough (throttle) to maintain a good heat rise or flow through the exchanger not too much, not too little.

Take the return header off, and check to make sure the tubes are clear (water chemistry).

Take the filter element out and run. You would be looking for a pressure considerably lower than what you have with the filter in. This may be easier to do than the removal of the header, and would rule out the exchanger tube blockage (water chemistry).

I keep saying water chemistry... What would be happening in this case would be if you were, for whatever reason, having a scaling condition (with the water) in the heater that would begin to form on the inside of the exchanger tubes eventually pinching off flow and causing the heater to overheat. I used to have a picture of this, but can not find it right now to show you, sorry.

Hope all that makes sense...

 

[hanesian]

A belated thank you for that very detailed and helpful response, Pool Clown. I just returned from a week out of town so am just now catching up.

I have a replacement internal bypass valve and it looks like that was definitely needed, as the current bypass valve was essentially stuck. There was also clear evidence of sand or silt inside the header, which may have contibuted to the bypass valve failure.

I am also now concerned that in additon to the bypass valve, the unitherm governor also needs replacing. I've tried submerging it in very hot water but cannot see any movement whatsoever, as it appears to be essentially rusted or fused. Here is a photo of that.

So my plan is to return to the pool store in the morning to get a new unitherm governor as well, before reassembling the header unit. I'll also try to examine the flex piping for any internal separation, and will put replacing that flex piping on my growing 'to-do' list!

The exchange tubes themselves look fairly clear, albeit just a bit rusty, so apparently water chemistry isn't my prime suspect right now, as much as those two worn out parts, and possibly flow issues in the flex piping.

Thanks again for your comprehensive response. It was very helpful, as was Paul's earlier response. I really appreciate all the help!

 

[ps0303]

Yep looks to be the issue.

When you put it back together, you don't need any teflon tape on the threads for the unions. Put some lube on the orings and you should be good to go.

 

[northsideirish]

Glad to see this. In my case it was the bypass valve. It was completely filled with the inert ingredients from pool shock. I pulled the header off, cleaned it out, flushed the copper core, and scraped out all of the junk from the bypass valve. Put it all back together and it works like a charm. I'm guessing the inert stuff came from me not putting my sand filter in rinse mode after flushing it. At any rate, it was not hard to do, and I'm glad I took the header off and didn't just try to clean the valve separately as there was some junk inside the header.