Help! - Boiler keeps cutting out

[PJL]

Hi, wonder if anyone can help with this problem...
I intended to drain down my C/H system to fit a new rad upstairs. Looked for a low point drain but there wasn't one - its a micro-bore system. Tried to drain from a drain cock on (what turns out to be) the outlet pipe from the wall boiler but only a few drips came out. Ended up draining system upstairs from the removed rad valves. Refilled system, bled rads but now the boiler (Potterton 60B) cuts out about 10s after start-up. Suspect there is an airlock in the system but I don't know how to get it out. Any ideas anyone??

 

[Rydell]

We need to know if its a sealed system or open vented? Meaning is there a F/E tank in the loft or do you have an expansion tank on the pipe work? The way to remove an air lock is different on either system.

 

[PJL]

I have a F/E tank in the loft. Used this to tip in a bottle of C/H protector when I refilled.

 

[newbie1]

its going to be long winded..what happens is the air is causing the boiler to overheat so it will keep cutting out
you will have to keep venting the rads as much as poss and you should also have a couple of vents near the hot water tank..i wouldnt suggest venting via the pump unless you know what you are doing
have to be careful the pump doesnt keep running dry as well
the air will vent just be patient

 

[stevetheplumber]

if the pump is seperate from the boiler you could try running the system without the boiler switched on for a day or two then vent everything
otherwise its a case of getting a hose conected somewhere and filling from the main micro bore can be a pig to refill

 

[Puddle]

Another option is to try reverse circulation, isolate and remove pump then fit opposite way round, let run for a hour then refit correct way, can work wonders

 

[PJL]

Thanks for the advice guys. Guess I'll try to keep venting through the rads with the pump on. Wasn't sure whether the motorised valve would direct water through to the circuit whan the boiler wasn't lit? Also, there is a 'vent' just before pipe connects to cylinder coil but this only has a screwed plug in and looks like it will produce a good fountain effect in the airing cupboard if removed!

 

[Puddle]

Yes the motorised will work normaly even when boiler off
is the vent before the cylinder on top pipe going into cylinder coil ,is it a scewed plug or a cap like fitting,is it brass,if so unscrew slightly maybe one half a turn ,wiggle about hopefully you will hear air coming out close when water dispersed,if you get air out try in pump on and off position

 

[REDSAW]

thats where you bleed the air through by slightly undoing it 1/4/turn should be auto-vent,

 

[Puddle]

thats where you bleed the air through by slightly undoing it 1/4/turn should be auto-vent,

Hi Redsaw

Am just being carefull as pjl said 1/4 plug fitted therefore thought maybe a auto vent was there once but been removed and plug fitted in its place

 

[Rydell]

One way I have used sometimes on difficult airlocks on a open system is to connect a rad valve to the mains water supply then push on a speedfit cap on the vent at the F/E tank, with help from your mate open up mains water for a short burst, 5 secs at a time. Air will be forced through the pipe work up to the tank against the pressure of the level in the tank! This does work but you must be careful of the level in the F/E tank it could overflow but the level would release through the overflow

 

[PJL]

Puddle,
Please advise what you mean by 'in pump on and off position'. Also, there is a valved bypass(?) line between cylinder coil outlet line (to rads) and pump discharge (connecting between pump and motorised valve). Should this bypass be opened for venting? Finally, yes the vent is before the cylinder on top pipe going into cylinder coil and the plug has a (v. large) screw-slotted head - looks more like a blanking plug, as head of it is hard up against female fitting. Don't know if there was ever anything else fitted there. One thing, my system has no vent pipe up to the F/E tank unlike all diagrams I've seen for open-vented systems??

 

[Puddle]

The bypass is there is allow water circulation via pump over run around boiler when motorized valves are closed or system turned off at high temp, for the work we are doing now, trying to dispel air the bypass should be closed, and this gives more water pressure around system
The fitting you mention with brass cap with slot in a manual vent, it requires opening with pump off then with pump on, the slot is for a screw driver to open but usually to tight so you will have to loosen off with a pair of grips on edge of nut, if you have not done this yet, by doing so my solve your problem, once vented let run for 1/2 hour and then see if circulating ok
If not as regards pump trick, you have to isolate pump each side using isolation valves fitted and actually physically change it around so it is flowing in the opposite direction, this helps with micro bore as any air locks in return pipework will be forced back into nearest radiator
But open cylinder vent first, once vented good chance you will be ok
And remember to open by pass when finished and return any other valves /controls to there original settings
The vent and cold feed maybe combined in these kind of systems

 

[PJL]

Thanks for this advice Puddle. Bleeding at the cylinder did the trick. Central heating fully operational now! Had to buy a replacement cap for the air vent - wouldn't re-seat properly - but managed to change this without much problem.