Hi there - I'm sorry to hear about your leaking collectors. Our collectors can certainly be repaired, using one of two methods that bypasses the affected tube(s).
The first method would be to use rubber repair plugs, which are inserted into the top and bottom of the affected tube. Repair plugs are available at several online retailers, simply search for "Aquatherm Repair Plugs." Be sure the plugs are meant for Aquatherm collectors, and not FAFCO. The difference is our plugs are 8mm wide while FAFCO plugs are 6mm wide.
The second method is to use widely available #10 or #12 stainless steel sheet metal screws to block the tube directly at the header/absorber weld. There's an explanation
here.
Personally, I would recommend the screw repair over the plug. The reason being, in areas where a hard freeze is an issue, the plug at the top of the collector will allow water to be trapped in that tube, even if the system is drained. When that happens, that water will freeze, and expand, causing a slug of ice to force the plug out over time. You don't have to worry about that issue with the screw method.
I would advise against trying any kind of sealant or adhesive. The polypropylene collectors are specifically designed to shed any kind of scaling - no sealant will stay adhered to them. Also, any attempts at using a sealant would technically void the manufacturer's warranty.
Best Regards,
Dan Sizelove
Marketing Coordinator / Customer Service
Aquatherm Industries, Inc.