Just for information BAXI 105E

Good for you. Many folk would have scrapped it for the sake of a part costing less than a pint. Of course the value of the time to fix is another matter, but it is yours.

you may also have seen an open cct accross the coil terminals vs a few hundred ohms, if it was an open winding. Equally the winding may be intact, and the mechanics of the contact rockers have rubbed though at the bearings after thousands of operations.

for relays of an age, in my experience of such things, the corrosion to open circuit of the coil windings  - which use surprisingly thin wire-  seems to race mechanical failure of the contact rocker. Corrosion wins in the cold and damp, but mechanical wear out for things that click a  lot in dry dusty places.

Mike.

Yes, good for you +1. You wouldn't have found a heating “engineer” who had the knowledge, competence or interest to do what you've achieved. Most, especially that national brand, who's name sounds a bit like a hideous seventies disco trio, would've said your combi was obsolete and flog you a new 'un for £5k (special offer)

Apparently it is a common fault which Baxi have known about for years, hence the revised pcb issues during boiler production. My pcb is dated June 2001. It is a shame that I cannot find a schematic or drawing of the Honeywell pcb, or at least a component designation for each item function. The 2nd pcb is a newer version I picked up for £29 off ebay but would not work when I swapped old for ‘new’. I don't know what the problem is with it though.

I can hear plumbers all over the land shouting “What are you doing? Boilers are the preserve of the Gas Safe Cartel!” Well since I didn't break any gas tight seals to access the boiler electrics I don't know how they can complain!

“Ah!” they shout, “And what will Baxi say about you modifying their pcbs unofficially?”

Well any warranties ran out decades ago, so there!

I can hear plumbers all over the land shouting “What are you doing? Boilers are the preserve of the Gas Safe Cartel!”

And, if you had charged a customer for doing gas work, they would be correct to do so. However, even if you had opened the flue or a gas-way, working for free, and on your own equipment no less, the only  legal compulsion is to be competent, not to be a member of a register of competent persons or to hold any particular city and guilds results.. Now of course if you break something, or in the limit gas yourself or burn your eyebrows off, then perhaps you were not competent, and as well as needing it sorting out suddenly it becomes illegal as well, but clearly this is not the case today.

As you call it a cartel, actually it is quite informative to compare the rates of gas accidents in the decade  before and after the introduction of compulsory Corgi registration, as it was called when it came in in 1992. (Corgi set off as a non-statutory trade body in 1970) Rather like part P, it cost quite a lot of money and had no great effect on the overall accident trends. 

Mike.

That boiler repair report is of interest to me and of value. I have friends with a problematic Alpha combi gas boiler. We had gas engineers attend recently but they mis-diagnosed the fault. I suspect a faulty relay with welded contacts that keeps the central heating pump running even when the control knob only calls for hot water. On fleabay a guy repairs the circuit boards for these boilers and sells them for a fraction of the cost of a new board.

Z.

I suspect a faulty relay with welded contacts that keeps the central heating pump running even when the control knob only calls for hot water.

With most combis it's usual to have a single pump that's used for both CH and hot water - when hot water is called for a diverter valve changes the flow from the pump away from the radiators to an internal heat exchanger that then heats the hot water - the hot water (DHW) isn't directly heated by the gas burner. There's a whole chain of events that needs to go right for correct operation - a pump running continuously could just as easily be caused by a stuck microswitch that detects hot water flow (usually on the diaphram valve) or a faulty overrun timer.

   - Andy.

mapj1: 
I can hear plumbers all over the land shouting “What are you doing? Boilers are the preserve of the Gas Safe Cartel!”

And, if you had charged a customer for doing gas work, they would be correct to do so. 

It wouldn't surprise me if you had difficulty getting a new board (or any other spare part) on the basis of not being gas registered. Thermocouples are, like brake pads, something that needs periodic replacement, but Screwfix will not sell them to me.

I didn't know that you could not work on boiler electrics for hire or reward even if you didn't remove any gas-tight covers. Surely you don't have to be Gas Safe registered in order to take off the front cover to connect in the mains supply and any control wiring do you?

I was going to look at getting a new boiler, and thought I'd fit it to the wall and just let the Gas Safe bloke come and connect up the gas side. So are you saying that a new boiler or any spare parts cannot be purchased online without the provision of proof of Gas Safe membership?

whjohnson: 
 

I didn't know that you could not work on boiler electrics for hire or reward even if you didn't remove any gas-tight covers. Surely you don't have to be Gas Safe registered in order to take off the front cover to connect in the mains supply and any control wiring do you?

I was going to look at getting a new boiler, and thought I'd fit it to the wall and just let the Gas Safe bloke come and connect up the gas side. So are you saying that a new boiler or any spare parts cannot be purchased online without the provision of proof of Gas Safe membership?

I used to fit my own boilers' and get a corgi, (yes back then…), to connect the gas, never had a problem BUT, nowadays' you are not allowed to removed the sealed cover, or tamper with the gas supply.

As for fitting the flue… I have been told, many times, by ‘plumbers’ that all you need to be is, as stated above… ‘competent!'

AJJewsbury: 
 

I suspect a faulty relay with welded contacts that keeps the central heating pump running even when the control knob only calls for hot water.

With most combis it's usual to have a single pump that's used for both CH and hot water - when hot water is called for a diverter valve changes the flow from the pump away from the radiators to an internal heat exchanger that then heats the hot water - the hot water (DHW) isn't directly heated by the gas burner. There's a whole chain of events that needs to go right for correct operation - a pump running continuously could just as easily be caused by a stuck microswitch that detects hot water flow (usually on the diaphram valve) or a faulty overrun timer.

   - Andy.

I thought that the hot water is moved by its own pressure from the potable cold water main though the heat exchanger to the taps, and does not need pumping. 

Please see illustration 2.10.

Z.