central heating flush issue

[John.g]

So the right hand (red) pipe actually goes into the bottom of the boiler and the left hand (blue) comes off the top of the boiler?? and the pump is on this (red) return pumping Upwards?.

 

[coolideas]

So the right hand (red) pipe actually goes into the bottom of the boiler and the left hand (blue) comes off the top of the boiler?? and the pump is on this (red) return pumping Upwards?.

The boiler has two pipes(obviously) coming from the top so I have no idea which is which! I went by the red tape that was on one of the pipes, but when I re-established the flow from F/E tank the water came out of the pipe marked red, which I had disconnected to .
Unfortunately the guy who installed the boiler is not a plumber and he was the last guy to try and fix the non working issue but obviously missed all the issues I found. He has said he doesn't want to do any more work on the system, I'm no

If it was pumping back through boiler flow that is dangerous as theres nowhere for the super heated water to escape up through vent, it would also explain the air being sucked in that way. If the hot water cylinder is venting over then that suggests the water is too hot, again dangerous as this could build up and eventually cause header tank to collapse releasing many litres of scolding hot water down through the ceiling.
This happen in my town a few years ago, although due to a faulty immersion heater but the end result was a toddler was killed in their sleep.
The more you find and say the worse this sounds.
Honestly I'm at the point now where all I will suggest is isolate system and fully upgrade after Christmas, it will be a nice job for you, a good little earner but this sounds incredibly dangerous and what you have to remember is you're the last guy to touch it, effectively making you responsible and liable. Personally I would walk away from this, it's not worth the hassle.

Thankfully they don't use this side of the house, it's rented in the summer and a teacher in one room for the school term. So heating is off now. I'm pretty sick of it myself, every day something new turns up!
I'll do more investigating this week to try and clarify which pipe is which etc.

 

[John.g]

Its amazing what "systems" are out there. a few years ago a neighbour of mine mentioned in passing that he would find the hi limit stat (Firebird oil boiler) tripped out on some mornings, he had had the circ pump changed out about 4 years previously. I eventually had a look and found that the replacement pump which replaced the original one also installed in the flow was pumping downwards through the boiler so the boiler stat was actually measuring the return temp and consequently the flow temperature (going back through the return) was 10/15C higher than the set point, it was only when the boiler was off overnight that the very hot water was rising up through the boiler and tripping the hi limit stat, I just reversed the pump and all was well. This boiler, like mine has a 3 bar PRV fitted on top of the boiler. BUT if I didn't have the time there and then to reverse the pump, I would have insisted that the system was shut down and remained so until rectified.

 

[SJB060685]

There you go John, a classic example

 

[coolideas]

Its amazing what "systems" are out there. a few years ago a neighbour of mine mentioned in passing that he would find the hi limit stat (Firebird oil boiler) tripped out on some mornings, he had had the circ pump changed out about 4 years previously. I eventually had a look and found that the replacement pump which replaced the original one also installed in the flow was pumping downwards through the boiler so the boiler stat was actually measuring the return temp and consequently the flow temperature (going back through the return) was 10/15C higher than the set point, it was only when the boiler was off overnight that the very hot water was rising up through the boiler and tripping the hi limit stat, I just reversed the pump and all was well. This boiler, like mine has a 3 bar PRV fitted on top of the boiler. BUT if I didn't have the time there and then to reverse the pump, I would have insisted that the system was shut down and remained so until rectified.

Systems over here are appalling, I have had to sort out two wrongly plumbed systems here this year, this is the third.
The last one, had a new bathroom installed with a raised floor, the floor rotted after a year so I was called in to redo it. The water came through 1/2" pipe from a tank with about 6" head into a shower pump (3/4") inlet and two sinks, two toilets and the shower! Pump was sitting on the hardboard ceiling of one of the toilets, loud every time it came on.
In that house they had disconnected the supply to the F/E tank as it had cracked, the owner was taking 5lit containers into the loft to fill it! Honestly you wouldn't believe the stuff that goes on.