back boiler issues

Hope someone can assist...

I have an old back boiler.
It's a baxi bermuda with a typical old style 70's grill front.
It started tripping the power off- allowed me to turn it back on once- then did it again the same evening, though this time it would NOT let me turn it back on (with it plugged in)- so every time you power on the boiler, it trips it off. The plug it connects to is fine (tested with other items), and a new timer has been tried and it did the same thing- but without the timer element on (so it's literally just on or off) it stays on and you can hear the boiler fire up and the power doesn't trip off! (so definately nothing wrong with the plug).
The plumbers i've had round are convinced it's my circulation pump but, after an extensive hunt for it in the house, we've been unable to find it. It's a gravity fed system so it must have a pump [they say].
So- questions to you guys is basically to ask about this issue as a whole: is it the timer and it's just wrong for this system? (currently a drayton LP522 digital timer); is it the pump?; if it's the pump- any idea where it'll be?!?; what could be suddently causing the power to trip?- if it isn't the timer or the pump?... anything else??!??!?!?!
Any suggestions/help will be gratefully received!

from Nik.

I will assume you have a typical setup of gravity Hot Water system/pumped central heating. Does the boiler fire up ok when hot water only is selected? This would indicate no fault with the boiler, and point to the pump. If HW working ok, switch on the heating, if it trips then pretty certain its the pump.

As to where the pump is, can be almost anywhere... Possibly under the floor, behind a panel on the side of the chimney breast, I know of one on this type of system in the understairs cupboard, completely remote from the boiler....

I don't get chance to select "hot water only" cause it trips off straight away- it only stays on when the timer is taken off (so no way to select the options). Though when it was working the timer didn't seem to make a difference- whether it was on heating, hot water or technically "off"- when the timer got power, the system was on and rads etc warmed up. (when it was working I selected "hot water only" to find the radiators still got warm. once asked someone servicing it about that and they basically said it sounds like a fault with the pump... maybe I should've taken this as a sign!)

As far as can see, it's just a standard gravity system. nowt fancy.

LP522 is fine for either gravity or fully pumped systems, just needs to be set up for whichever type it is to control. You said you've tried a new timer, what was the previous model? The LP522 will work ok as a replacement for some types, others will need some alteration to the wiring.

If the boiler is firing up ok without the timer fitted then that rules the boiler out, and points to the pump (or other controls if fitted). How did you supply power to the boiler with the timer disconnected?

~our pump is at theright hand side of the chimney breast as is the timer switch~
Does anyone have any experience of replacing Baxi Bermuda system(5sc)~ours is from 1972 and needs a gas valve but unable to source~ with the new Baxi Bermuda BBU HE? Approximate cost?does it work well?

andmcit said:

~our pump is at theright hand side of the chimney breast as is the timer switch~
Does anyone have any experience of replacing Baxi Bermuda system(5sc)~ours is from 1972 and needs a gas valve but unable to source~ with the new Baxi Bermuda BBU HE? Approximate cost?does it work well?

Click to expand...

i would suggest you need to widen your search, the gas valves for these are the back bone of the industry and are available from ANY/EVERY heating supplier, and i would go as far as to say if you set a poll up on here on how many guys reading the post had a new valve in their van/stock the % would be high

Not on a 1972 model they woldn`t that would be a 572 and used a thermo electric valve to hold pilot open and a stephenson valve and resistor to allow main gas to come on.
And not been properly avialable for at least 15 years

Thank you! that's very useful information and describes the system we have. The thermocouple, thermostat and resistor are all okay.
Can you or anyone please advise who can supply me with the stephenson valve ( new or old!!!) that I need~ any help would be most appreciated.
Failing that, is it possible to dismantle and repair the one we have ?