Teledyne Laars Mark V - Is it safe to disable bypass valve?

[mnschu]

I have an old Teledyne Laars Mark V heater that is still ticking.
It was working fine until recently, when turned on it starts to knock and vibrate like crazy when it heats up.
I checked the bypass valve inside the inlet/outlet header, and it was not all there.
This valve seems to work by having a spring push a plate against the opening between inlet and outlet, this spring and plate is located on the outlet side.
Surprising, I did find the plate only for only $14 online, so I ordered.
All the other parts seem to be intact.

However, I have my doubts about re-building this.
There is a lot of rust inside, and it seems the original plate breached into the inlet side.
If that is the case, this header is not usable with the original bypass valve as the opening would be too big.

I am wondering if I can do a temporary fix until I buy a new heater.
I was thinking of just sealing the hole between inlet and outlet, thereby removing any internal bypass.
We only use the heater for the spa, and will be there to manually turn it on and off.
If I did this I guess I should also plumb an external bypass so under normal filtering I bypass the heater.

Is this a potential safety issue? Could the return water be too hot?
If so could I partially open the external bypass to cool it down some?

If anyone has some feedback or good advice please reply.

One other note. The manual says the bypass plate that I am missing is made of Lexan, a type of plastic.
Anyone know about Lexan? Will this last forever and it is still in my plumbing somewhere, or has disintegrated and broken to pieces? What are the tricks to find these items?

 

[ps0303]

Don't waste your time. Purchase a new heater and be trouble free for a while. A great replacement for this unit would be a Raypak/Rheem.

 

[mnschu]

Let me give an update:
I received the bypass valve replacement from poolsupplyworld.
It is a disk shaped piece of plastic with a shaft.
After removing the inlet and outlet pipes, I could see into the outlet area and found the what remained of the old bypass valve. It was just the shaft portion, the plastic disk part must have been broken off over time.
Also, the insides of the intake enclosure did show signs of rust and some buildup, but for the most part, it was well intact and still functional. I believe these are made of thick brass.
I was able to install the new bypass valve, but I did have to cut the spring down, as it was stretched and pushing with too much force.
I put back together and the heater is now functional again.

I do have a very small drip leak at the output manifold. This is metal on metal, and I did not have any gasket material. I tried to reuse what was there and some silicone, but it did not work. I plan to cut a gasket from gasket material, I expect it will fix this.

The heater is also working a lot better than it used to. Before it began knocking, it would run for awhile and stop. Then run for awhile and stop. Now it runs until hitting the temperature on the thermostat.

These Laars Teledyne heaters are industrial grade, they seem to last forever.

I see many on the forums recommending Raypak, why do people prefer this over Laars (I guess this is Jandy now)?
I still plan to get a new heater, so trying to decide on what brand to buy.

 

[ps0303]

The Raypak closely resembles the Laars. It doesn't have any extra parts like a blower motor or extra boards like many other models do. Also since you have a Laars, not much has to change for installing a Raypak. Also Raypak has a better track record so far against all of the other brands out.