ANOTHER Riello RDB question (forum checked, can't find similar)

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Hello all
I have firstly checked the forum (and others) for RDB advice and I am now fairly familiar with the unit, but still can't find what specifically is happening. So back to basics:

I let the tank run out (no criticism please, no one does it on purpose, some of us are not having an easy time). I had it re-filled. I am already familiar with the bleeding process as I did in fact let it run dry a year back. On this occasion, it did fire up, but stopped after a day and now won't fire at all. One thread on here described that same symptom but his was a knackered pump- as I'll explain below, I don't THINK that's my issue here.

There is a single 240V cable from the airing cupboard to the boiler, which in turn feeds the pump. The power is there and the red lock button is illuminated. After releasing the bleed screw and pressing the button, the fan operates for several seconds and then the solenoid for the pump clicks. I believe I have bled it properly and there's no air now. As an experiment I did loosen the screw quite a long way out to see if I could determine pressure and it gave a nice blast, so I don't think the pump is failed. I was then advised to take out the photocell and keep my finger over the end of it- I also tried it shining a torch into it, but neither made any difference. I understand there's a PCB there, but I'm not a big fan of co-incidences and that "something" just failed at the same time as I ran it dry. Therefore my first question is whether there is anything that is susceptible to failing as a result of 'drying'?

I know it is popular to suggest that empty tanks will draw in water and debris, but like on the commercial vehicles I repair, this is a phantom. The tank outlet is always at the bottom (or in this case about 1/2 inch above) and that is where it draws fuel out whether it's nearly empty or if it's full. In any case I did collect some of the spillage and left it in a clear glass and there's no sign of water and oil separation or any debris, so I don't think my problem is the tank or the filter or the pipe.

As someone put this already from a previous comment- these are not rocket science (well actually, there's a similarity, but...) I am quite happy with the idea of removing it and doing whatever is needed, but there's obviously something I'm missing. I am tempted to disconnect the fuel pipe and try to draw oil from a clean container just to be 100% sure about the feed, but I am reticent to break the seals and have to go through bleeding it all again.

Any advice would be appreciated. Unfortunately calling an engineer isn't an option for me right now. Now that I've found this forum, I will happily apply any knowledge I have to help others from my own area of expertise, which is mosty welding, joinery and diesel engineering.


Kind regards and festive greetings.
 
Can you post the control box type/details.
Is it a 1 pipe, 2 pipe or tiger loop oil supply?.
 
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