My pool heater is a Purex Tropic Isle Model 180, pretty old I think. It has just begun to leak. I located the leak in what I think must be the thermostat, a three/four inch copper tube which screws into the heat exchanger. Two wires come out - one goes to the on/off switch and the other to the pressure switch. When I unscrewed the tube with the wires attached, it was quite damaged and I could see a couple of very small holes. It's a Honeywell product.
Is it possible to get a replacement?

Thanks in advance

A copper tube with two wires on it?

Either this is a high limit sensor, or the thermostat where your description is confusing.

If this is a one piece unit with two wires - just a threaded device, then you'll need to replace it as it's become compromised.

If it's the business end of a thermostat, it'll be a 3" or so bulb with a copper capillary tube, 12-36" in length that goes to the dial control and that has two wires on it. You'd have to replace that for the same reason.

Best source for this is going to be a local pool supply store. Pull it, take it down there with a model number for your heater. If they've got local distro books on heaters, then they should be able to order you the part.

Being that's it's an 'ancient' tropic isle heater, (the old brown colored one), it's really time for a new heater though... imo...

The 2 x wires ,one to the on/off switch and one to the pressure switch would suggest it is a hi limit cut out that has been eaten out, but your description of a 3 inch copper tube suggests it is the heat sensor pocket that has been eaten out. We need more accurate information to be helpfull to you. I assume the heater has a standing pilot with a manual thermostat or could it be electronic ignition with electronic thermostat and maybe a digital or LCD display.