Thank's all for your replies.
To get around the problem, I:
1.Ordered a Brother colour laser - which works fine.
2.Ordered a new black printhead for the Canon G7020.
The new printhead worked - note that the printer was only used intermittently ( still managing to suck out ink at an alarming rate) and only got 600 pages before crapping out.
The lesson I learned was that I've finished with Canon products and regret having stuck with them from the ip3000 to ip4500 - BTW the new head cost Can $97 including tax and shipping.The company I dealt with is PGtech out of Montreal - same day shipping, kudos.
