HRM Wallstar air problem

Here's your spec, if the "fire valve & non return valve" are one, which they appear to be, then presume it is installed vertically as shown?, if the NRV isnt 100% tight then would imagine that the oil in the pipe below it could empty out down to the level in the oil tank and even though the pump can lift 2.5M then it would have to fill or at least partly fill this line again, by which time the burner may have tripped out even though it does a ~ 12 sec purge and then allows 5sec to flame detection. Maybe a very lightly loaded spring typoe NRV installed at the tank outlet may help?. If the boiler runs OK during the day but is inclined to trip in the morning after say 8hrs off then more time for the oil to drain back.

Re: the Tiger Loop, they merely say its not required but I would certainly look at installing one if my tank was well below the pump as the tiger loop is a deaerator.

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yes it is vertical, top of tank to bottom of boiler is about 1/2m, present oil level to bottom of boiler is about 1.5m
The oil is pulled through immediately so must presume the NRV is working - it is a new Valspar one but is displaying the same as the old one did
no difference night or day
During the 10 to 12 sec purge period the pump will just be recirculating oil around itself, what happens to the bubble during this period?, after the purge period the solenoid vale will operate and oil will flow through the nozzle for at least 5 secs even if the burner then locks out, what happens to the bubble during this period?. If the oil is flowing "under" the bubble then does the bubble matter?
Is the burner actually locking out?.
during the purge phase the bubble gets dragged down towards the pump, if the bubble is big enough it will get sucked in to the pump and hence locks out
I appreciate that "they all do it " but surely ideally there should be ZERO air in the oil line
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I suppose its nigh on impossible to stop some air ingress (eventually) through valve spindles or whatever with the oil level below the pump, thats why they install a two pipe system (or a T.loop), even with your present bubble, if you could magically reinstall the internal by pass screw and run the recirc pipe back to the tank then the bubble would dissappear probably in a few seconds during the purge period since it would pass straight through the pump and back to the tank. With the single pipe it wont/shouldnt be pulled right into the pump until the solenoid operates and there is a flow through the nozzle.
The large static bubble is something I have lived with since installation some 27 years ago o_O.....but clearly something is now wrong as it gets bigger by the day.....but, despite the efforts of myself (a highly competent DIYer who put the thing in) and my HRM engineer we just cant figure out what the problem is

next thing to try is coupling the clear pipe directly to the incoming oil pipe bypassing the fire and NR valve to see if the bubbles still happen.....

cant really see the point of the fire valve anyway as, should a fire happen and the pipe melts the oil will simply drain back to the tank....I can fully understand it's purpose if the tank was higher than the boiler.......but it isnt
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Static is the word, I had a "glass" filter on my tank outlet for about 16 years until I changed it to a alloy type a few years ago, there was no air vent, you just screwed the glass into the filter base, consequently, there was a bubble of air in the top of the filter which took months to dissipate so its pretty obvious that you now have a dynamic bubble, even though your problem is interesting and all that I am a little surprised that they at least don't suggest a two pipe or T.Loop for a system like yours, air ingress then wouldn't be a problem but I can see where you are coming from. I have quite a lot of DIY with my relations and my own oil fired systems which I find to be outstandingly reliable and trouble free, my own is over 18 years old and (no joking) has never locked out on combustion failure in this 18 years, my daughter's 2/3 times in over 22 years, key to it IMO is never let the pump run dry due to running out of oil.
I think, with over a ton of oil in the tank that any air would soon be moved up the pipe to the highest point
Also you get a few small bubbles if you tap the fire valve....exactly the same as on the one it replaced - and yes, I bought a decent quality Valspar one
Is the oil level in your tank when filled above the pump suction and if so how far does it have to drop before its below the pump.
Maybe the Kerosine characteristics have changed over the past 25 years or so and it releases air more readily or something like that?, even so, any air content thats released has to pass through the burner in one form or another to get rid of it with a one pipe system.
just observed this.... the pipe at the back is the one going into the pump....micro air bubbles are coming back up the pipe when its can they be coming up when the oil is going down ???
The pumps capacity is far in excess of the required burner flowrate so the excess is recirculating around the pump in the one pipe system with a lot of turbulence so maybe releases some entrained air in oil? but this never causes a problem generally, the only way it couldn't recirculate is if the bypass screw wasn't removed from the pump but this would result in huge pump pressures and rapid seal failure or worse.

Why is the plastic pipe above the pump?, couldn't it be fed in underneath if that would make any difference.

Why is it only this boiler make has this plastic pipe?
dunno....thats obviously the way they have been designed.....
Because it is a wall mounted boiler that is generally fitted above the tank level and designed to run on a single pipe without a deaerator. A clear pipe enables you to see any airlocks. At one time clear pipes were fitted to Trianco boilers.

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