No hot water but no fault light

Hi, since we got back from a holiday, we no longer seem to get hot water from our A Class boiler. We knew as soon as we got back that we needed to check and top up the grey manual fill tank above. But we have no hot water, even when pressing the boost button. The fault indicator is not showing anything. We are not on Economy 7.

We've been in the property for 3 years and have had this problem before, have had maybe half a dozen engineer visits. They always say nothing is wrong, occasionally replace a part "just in case", mostly just fiddle about with it and then the hot water is back, with us none the wiser about what the issue was.

This time before resorting to calling someone, we unscrewed the front panel and initially I pressed the S1 and S2 buttons a couple of times. The display above went from two lines to flashing numbers and the boiler started making more noise. After about an hour we had hot water again! This lasted for about 24 hours or so before the water went cold again.

I have tried the S1 and S2 buttons, I have done the 10-second S2 reset, but I must confess, even with the manual, I'm not expert enough to know what to make of it. I have seen various numbers flash up, including the 33 which I gather is some kind of appliance selection fault, but I neither know how to deal with that, nor whether that is the fault code or one of the other numbers.

As we are just weeks away from our wedding, we don't have money to throw at the wrong solution or get another temporary fix in place, when I can't help feeling it might just be a setting issue or an easier fix. Please can anyone advise? Is there any hope or are we best off forking out for a new boiler?

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Go through the fault codes step by step, take your time.
If not on E7 then check the unit has a supply.
There are relays x 2 and an interface relay.
There are relays on the main board too.
Mike

Thanks Mike, location updated.
I have cycled through the display flowchart carefully and I am getting a code 33 for both fault code lockout and blockout, followed by FF (fault location empty?) for each of the right-hand cycles of the S1 button. Sensor temp ranges between 29 and 33.
To tackle the 33 'appliance selection' code, I have tried re-setting the appliance and choosing a different code, but it doesn't like any of them. With the exception of the first one (03 I think), the rest all result in both error lights coming on. If I put it back on the first appliance code, the error lights disappear but no improvement to the temperature of the water. I'm not actually sure how to work out the ID resistor it should be matched to?
Could it still be the supply? I have located the off-peak circuit fuse holder but how exactly is the fuse accessed, and does it look like a normal household fuse?
I will use the schematic to investigate the relays further if you think it's still worthwhile, though these were replaced 'just in case' the last time the boiler let us down.

I don't really want to give up just yet, but if we end up needing a new boiler, are we limited by what types we can get? What would you recommend looking into? (There is no gas in the property.)
Thanks again.

Hi ya,
Look on here for Mario.
Ex Gledhill engineer.
Cover your area I think.
Mike