alpha CB28 combination boiler

New to this site, but could do with help with my boiler !
My boiler is not switching on and staying on.It started about a week ago and I looked at the lights on the front panel. The bottom indicator neon is flashing every second, so after consulting the alpha helpline they said it was a temperature sensor fault. I had the part ordered and fitted last night by a plumber who admits he hasnt had a lot of dealings with Alpha boilers. The boiler still didnt work immediately, it was firing up and the light was coming on constantly for a few seconds and then going off and back to flashing every second.
After an adjustment on the fan he managed to get it going again, so I had hot water and heating for the first time in over a week.
However this morning it has gone off again, the light is back to flashing every second. I have tried pressing the reset button a few times but nothing is happening. Sometimes it fires up for a few seconds and the pipes start to get hot but then it switches back off.

Can any one help, its starting to get cold on a night !!!

Does it do it on both heating and hot water or just one not the other?

Had the boiler been unused for a while?

Is the system water clean has it always been clean is their a chance the pump/heat exchangers could be partially blocked?

He change a thermister? or both thermisters? if a thermister hope it was primary.

If original was white won't have been the fault.

If primary thermister changed and trusting diagnostics are right it will be a problem with the pump or sludge. This should be investigated first. Then consider diagnostics are wrong it will be the pcb in the first isnatnce as it is fualty anyway but that doesn't mean there is not a fan aps fault which is being masked by wrong diagnostics. As you said your plumber fiddled with fan (which has no adjustment, though aps does however it should not be adjusted). This boiler would on;y suffer problems with fan venturi after many years faithful service and a lot of hard work. There is a metal tube into the fan cowling with a small flexible hose that goes to the aps, this can easily get a moths wing across it or cobweb spun across it, so it needs a clean. These aps's are seldome needed, I never changed one in two years covering these boilers. Changed one fan for this model, all the rest just required a clean.

Thermister faults from diagnostics were always wrong the true fault was 99% of the time sludge, the other 1% was a pcb throwing up spurious diagnostics so it had to be changed but the real fault then has to be discovered.

The diagnostics are crude I never relied on them.

It does it on both the heating and water. The system is due a service and I have booked one in for this weekend for the whole system.
Forgive me for not being too technical I am not an engineer of any sort just a mere female from Durham so it was nice that a Yorkshire man replied to this plea for help - us Northeners are always the friendliest !!
The plumber I have at the minute is someone a friend has used and is one of the few who isnt ripping my eyes out, being female if you know what I mean. He is corgi registered but like I said before admits he hasnt done much work with this boiler before. I was recommended this site from someone at work who got their problem fixed from it. I have told the plumber I was going to ask for help and he was grateful of any advise anyone could give as he was thinking big parts and big money to repair it.

No it should be economic to repair.

Mehran lives in Hartlepool he could fix it as he is Biasi and Heatline service agent so a Alpha cb28 shouldn't present him with massive problems.

But why not phone Alpha and ask who is their local service agent and can they refer the job to him. I say this because for that guy this will be easy peasy.

Myself I am tied to British Gas and mostly in Hull these days though I love in Scarborough..

Alpha do a good service contract used to cost £12 a month get annual service and guaranteed fix.

Your boiler will need domestic hot water flow switches a few times in it's life and a couple of times a diaphragm, anual servicing and very little else if your system water is clean.

Thanks very much for that I will ring them tomorrow and find out more about it.
I will let you know how I get on

Myself I am tied to British Gas and mostly in Hull these days though I love in Scarborough..

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Now we know what you do in Scarborough, where do you live?