Well guys - it cost me £285. I watched the guy checking everything and it did turn out to be the gas valve. I know this sounds as if I'm a nightmare for being suspicious, but when he went to get the new valve, I watched him bring it in - in a new pristine box and and while I was popping in and out - doing other things - I saw him take out the old and put in the new. He worked solidlly all the time 1.30 to 5.30pm and did all the tests before and after. I did the 'discount for cash?'
He said that if he ever - and it was rare-ish - had to replace gas valves on these boilers, he'd had to order the part, but when he went to his supplier he was surprised to find they had quite a few in stock. His supplier said that he'd been selling a lot recently.
I probably should have opted for Potterton Heateam at £299 with a year's repairs - if you need 'em. But by the time he'd done the diagnostics I thought it would be mean of me. Besides the friend who's renting the flat has a baby and though I'd given them an electric heater, they had been without central heating and hot water for almost a week. So I didn't feel I could reasonably make them wait any longer
I tell you what I hate. It's middle class people on good salaries who complain about what they have to pay plumbers, car mechanics , builders, etc. I think its a weird kind of snobbery and indignation. They think other people (other meaning - not their own kind) should earn less than them. I'm not middle class, I'm self employed and work is unpredictable - I've got loads or not enough. The valve cost £150 - take off other expenses and my guy - a trained, skilled worker involving responsibility for potentially dangerous gas and equipment (who must be paying heavily for insurance and corgi stuff, etc)got £100 for half a day's work. Are these snobs really worth more - they are usually the same people who would say they are all for equality, would believe in animal rights, would criticize racists, sexists, etc. Just so long as they are on the top of the heap and seen as 'better' everything's ok.
Sorry about the rant guys.