Plumbing Question about Pipe Connectors?

My Plumber has just done a job for me. This was dis-connecting a radiator in the bathroom and replacing it with plastic Pipe Connectors (No soldering). The original pipework is the gravity feed pipes which supply the how water from the boiler which is downstairs. The advantage of this is to keep the towels dry when the central heating is switched off. However, these pipe connectors are chunky and I have reservations about their reliabilty being "push-on" and not soldered on. I therefore went into Wickes Store and bought one of this type of connector to try and understand how it worked. On the packet instructions it states inter alia that they are not suitable for gas, oil, compressed air or connection to back boilers and "gravity circulating heating pipes". So could someone out there who is knowledgeable in this field explain to me 'why not' and again will I have water seepage/leaking in the time ahead at some point ???

Public Comments

plastic plumbing pipes are for 'return' cold water only, usually used for drains, etc... they cant stand up to hot or high pressure water, you need metal soldered pipes for that...
plastic pipe should not be used for a boiler system. Copper pipe transfers heat very quickly, plastic won't. I've never heard of this being done before. If the original piping was copper it should remain copper. Personally I don't think plastic pipe or fittings will or would last in a heating system and would fail eventually.
CPVC pipe is used for hot water piping, this is a plastic pipe. Usually a temperature of 200 F is a max temp. As mentioned before plastic pipe is not a very good idea for a heating system. Here's a link to plastic pipe site for specs. http://www.harvel.com/tech-specs-cpvc-pipe.asp
You can choose PPR (Polypropelene) pipes Which is having resistant to High Temperature (110 C). It has good insulation property.