Confusing problem with Myson Apollo 50B

4 Mar 2004
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United Kingdom
Hi all,

I have recenlty moved house and the new house is fitted with an old Apollo 50B. Shortly after moving in I noticed the pilot light was not lit and have subsequently struggled to get it to relight.

I know this problem has been discussed before so I won't labour the point, suffice to say that when the pilot light gas supply is released after 20s, it goes out - the main supply never looks like kicking in.

I'm pretty sure I wanna try the thermocouple first. My problem is that I've just bought a thermocouple (THERMOCOUPLE THORN APOLLO TYPE) which apparently fits my boiler from plumb center. When my plumber has come to fit it, the thermocouple from plumb center has a two pin interruptor about half way along which the original one from the boiler does not have. He explained that this links the TC to a thermostat and pointed out that my boiler has two connections that take the place of this interruptor near by where the TC connects to the main circuit box (sorry, as my name suggests plumbing isn't my profession!!) so it seems pretty likely he's right.

That said both parts center and onlineboilerspares say that this part (incidentally, it's number is T99-700/1 or T99 - 700I (from Onlineboilerspares)) is suitable for my boiler. As per:

MYSON APOLLO FANFARE 15/30/30/50,15/30B,15/30C,30,50B,30/50C

This is the same quote on both websites.

I'd be really grateful if anyone can throw any light on this. Once I'd realised my boiler was an Apollo 50B I've been all round the houses looking up Baxi then Potterton and finally Myson parts. Now I'm sure of what boiler I'm looking for I'm completely stumped on this whats going on with these parts and I'm sure it will take one of you good guys approximately 30s to diagnose the problem!!

Any help at all much appreciated!!!!!


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Try a universal TC. You can get these from any supplier.I'm surprised that your plumber didnt carry one of these in his van! The TC can also be tested for a fault using a (would you believe it) TC tester.
Thanks for a quick reply. I'll be sure to look into that. As to why the plumber didn't carry anything of use....well. I dunno he's a mate but I suppose if he was going to have to come back again he might be able to make twice as much cash? Am I too cynical :D

Anyone got any ideas as to whether this T99 - 700/1 really should fit an Apollo 50B? I'd love to know what the problem is!
dont put yerself down. you can never, too cynical.

perhaps he was in a car?

;) :LOL:
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No. He was in a big van with his name painted down the side :eek:

UPDATE: Just been having another look. The :oops: circuit box I described the TC as going into is actually made by Honeywell. Is this common for a Myson boiler to have a Honeywell part or is it possible that at some point the old owner cobbled together two separate components and hence the TC I've bought for this boiler doesn;t fit??

Anyone got a manual for this boiler?

Thanks again
manufacturers part number for a apollo 50B thermocouple is:
Q309A2721 for the honeywell 18/24 tc or:
309S189 for the segas T2-26

Neither of these has an interrupter.
kevplumb said:
oh an appolo without an interuppter

do educate the great unwashed pleeeeese

well the overheat cut off is wired into the gas valve and the other spade clamped into the gas valve with the end of the a standard universal is fine.

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