Just Tested central heating -I think I have a air lock or blockage somewhere

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I have a Grant Oil Boiler - Vented system - 4 zone valves - two automatic bleed valves near the pump and H/W cylinder Upstairs and the Boiler is downstairs.
I started the system and set the thermostats to call for heat.
After a minute or so I kept hearing soft thump sounds from boiler, it seemed like water was being overheated.
I checked the flow pipe out of the boiler and that was cold even after a few minutes.
so
I checked the pump was running and that the zone valves operated.
I then checked that the c/h tank in the loft had water in it and that the stopcock was working.
I bled the Pump - small drips out of it but didn't hear any air.
I even cleaned the Magnetic filter to see if that might be blocked up.
I turned the pump up high and small drips of water came from both auto bleed valves so I think they have water in them ok.
Now I can't think what else to do.
I suppose pump could be blocked, it sounded ok but...

any ideas would be appreciated.

thanks

Mike
 
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ah! Didn't think of the obvious
I took the boiler cover off which is blimmin awkward and had a good listen a =nd look the Noise seems to be the Boiler trying to start so I'll have to rethink
 
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I don't think It's getting any oil !
Is there an easy way to check for this?

mike
 
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If the tank is higher than the burner, and all the valves are open, can you crack open a joint on the flexible supply pipe inside the boiler casing?
John :)
 
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Thanks
Was hoping there was another way ;( The Boiler is in a cupboard and extremely difficult to get to.
It looks like I will have to though.
I was looking for some sort of bleed valve but there is none mentioned in the manual and nothing obvious that I can see.

Mike
 
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Has your boiler got a Riello RDB burner, do you know?
It's easy enough to bleed, courtesy of a hexagonal bar that sticks out of the pump, with an Allen key socket in the end.
John :)
 
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yes I noticed that but the manual said it was a test point
Thanks
will try that tomorrow

Mike
 
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It is a test point Mike.....it's where you can fix a pressure gauge to adjust the pump.
Word of caution if I may.......don't adjust any screw on the pump, notably the one in the centre of a large hexagon nut, as that one changes the oil pump delivery pressure.
John :)
 
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If I have oil at the pump it would seem to be likely that the control box is faulty? is that right?
should I look at the electrodes maybe?
Is there anyway to test the control box?
I don't know anything at the moment but I have an electrical/electronics background so with the right info I could learn I think.
what makes me think that is I have just seen the control box for £72 quid lol
 
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The control box is quite a reliable item Mike, and I'm sure many have been replaced unnecessarily.....
Here's a typical burner start up sequence:
Motor starts, turning the fan and oil pump, ignition spark present but no burning ......this purges the flue with fresh air.
After a few seconds, the oil is electrically switched on, combustion starts. If a photocell sees light (flame) the oil supply continues, ignition spark stopped.
Typical regular faults are a dirty photocell or a faulty oil pump solenoid coil ( the part that allows oil to flow) so I wouldn't be throwing parts at the burner just yet!
John :)
 
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Cheers mate! ;) good advice methinks
How to test which part is faulty though without the test equipment.
or does it come down to replacing the cheaper parts first?

On the other hand I read something about a faulty photocell which said it would lock out after a few attempts.
Mine goes on and on it doesn't stop until i switch it off.
 
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Certainly, a photocell can fail in this way (it keeps the burner running because it thinks it can see a flame) and also it can allow the burner to start up, but shut down immediately afterwards (because it thinks it can't see a flame). Its certainly worth giving it a clean!
After that, I wouldn't start throwing parts at it just yet -do ascertain that oil is getting to the pump first.
John :)
 
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thanks mate
I did have another look last night ,I tried pulling the Photocell out. while it was out I tried to start the burner and it did ignite because without the cell in I could actually see the flames.
I covered the cell with my thumb and it started for for probably less than a second though.
But the interesting thing is that with my thumb over it I got the lock out button light up.
Now I don't get that normally so I think? that tells me the Pcell is ok?
I cleaned it anyway but with it back in it went back to multiple attempts at ignition with no lock out.

Yeah Oil is next I will see if I have some rubber pipe or something, Wife will kill me if I get oil everywhere lol

thanks mate
 
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At the moment you try to start the burner, keep the photocell completely dark - as it would be inside the boiler.
The moment the burner lights, show the photocell light (as per the flame) - and it should keep the oil supply on.
John :)
 
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OK
well I did try to bleed the oil but it wasn't the most elegant job (picture oil squirting back down past the hex bleeding post and all over the bottom of the boiler ;( )
Pipe was too stiff to grip it properly. so I really can't say if there was air in it lol.

So I thought it was worth another try to see if it had fixed it anyway so I tried starting the burner again... No go - same as before.
So I whipped out the photocell and this time I had my torch ready.
I started the burner with my thumb on the cell and the second it started I put my torch right up to the cell.......... and It worked!
it kept burning for as long as I held the torch to the cell.
I can only think the flames are not registering brightly enough for the cell but my torch is.
so I reckon the cell resistance must be a bit high without a very bright light on it.

new photocell needed ? that's what it looks like to me but I bow to you superior knowledge ;)

Mike
 
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