Alpha Boiler overflow leaking

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madworld | 00:40 Fri 25th Jan 2008 | Home & Garden
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I have an Alpha Combi Boiler (no tank). The overflow pipe outside the bathroom has water dripping out constantly. How can I stop it?? The pressure gauge is sitting at about 3 bar. I have heating cover will this be covered?


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Sounds like your filling loop (by which one would put more water into the primary system) has been turned on a bit and it is injecting water into the system. When the pressure gets to 3 bar the automatic overpressure valve is allowing the excess water out. Check the filling loop.
congratulations on owning the biggest bag of cack boiler ever made!

could be the filling loop not closed off properly or passing water, best way to tell is to try and make sure the taps are off then take off the one end of the loop and see if any waters still flowing through it.
other problem which is very common is the expansion vessel needs to be re-pressurised. on every combi boiler there is a metal expansion vessel which is usually bright red and circular and has a car tyre type valve on it. inside this vessel is a rubber diaphragm and on one side of this diaphragm there is air and on the other water. this vessel allows for the expansion of the water as the boiler heats up so it doesn't explode basically. if the diaphragm is damaged or the air has escaped then the pressure gauge will climb until it reaches a point where the pressure relief valve will open up and dump the water out the back of the boiler and thru the overflow pipe. you then have to fill the boiler back up via the filling loop. but unfortunately often when the pressure relief valve opens it doesn't shut properly again due to sludge and debris in the water getting stuck in the valve seating, this would explain why you get the constant drip.
an heating engineer can check and re-pressurise the expansion vessel if needed for you no problem at all. but if when he puts his pressure gauge onto the tyre type valve water comes out then it means the diaphragm has ruptured and you need a new expansion vessel which often means takng the boiler off the wall, a right pain in the backside job
oh i should have said, before you reply and tell me yours doesn't have an expansion vessel they are usually hidden at the back of the boiler and you have to remove the outer case and then look either down from the top of the boiler or up from the bottom of it.
Sounds incredibly plausible, Gucciman, and I know from other answers you know your stuff, but I just don't get this failure mechanism. How can a split in the diaphragm that allows water out result in an increase in pressure across the whole system?
thanks builders mate, you obviously know your stuff on a wide range of topics too, always enjoy reading your answers. i'm only a trainee heating engineer,but am learning from the best, my dad was at british gas for 35 yrs, 20 of those as a training manager teaching the apprentices and was acknowledged as british gas's boiler expert as every boiler sold in the uk had to go through him first to be stripped to bits and assessed so they could train the apprentices on them, ive been working with him for nearly 2 years now.
i will have to go into it in more detail with him as i'm still not sure of the exact mechanisms involved but basically the expansion vessel is half full of air and half full of water and the 2 are seperated with a rubber diaphragm. the air side is normally pressurised to around .5 to .7 bar. when the boiler is running and the water heats up the water in the system expands and fills the expanson vessel and presumably when the water cools it contracts in volume and the air side of the diaphragm must act as a spring and push the water back out (i'm trying to think logically here) so if the air side of the vessel is flat i.e. no air in it then there is going to be too much water in the vessel and no air to push it back out (logically i would have thought that would read as low pressure) no, i'll have to ask the old man!
anyway, the expansion vessel being flat is the main reason for the pressure rising and dumping the water out via the prv. when we check the air pressure in the exp vessel we close the heating flow and returns and then we open the prv and leave it in the open position. we check the air pressure using a normal tyre pressure valve and if needed add more air with a bike pump until we get the .5 to .7 bar. we then close the prv, open the flow and return valves and fill the boiler back up. this usually fixes the problem but if when u check the air pressure any water spits out the valve it means the diaphragm as gone and the waters in the side the air should be and the exp vessel then needs replacing as they are sealed and you cant change just the diaphragm.
Quite simply buildersmate, As water is heated it expands this expansion is usally taken up and accounted for by the diaphram of the expansion vessle. When a diaphragm fails it will either split and the the expansion vessle will fill up with water ( easily checked by the pressence of water at the air intake valve ) or it will over stretch and loose its elasticity ( a zero reading on the engineers pressure guage will confirm this ) Both failures will result in there no longer been any room left in the sealed system to allow for the heated water to expand so the pressure rises. The hotter it gets the more pressure is put on the system untill it reaches a critical level thus leading to the safety relief valve operating before any damage occours to system,home or person and dumping the contents of the system out untill the pressure has dropped down to a safe level. Gucciman is spot on with his diagnosis
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Apologies for not replying sooner. I have been ill since posing the question. Thank You to buildersmate, Gucciman and gasman for your excellent replies. Heating Engineer is coming out to have a look this week and I will try my best not to tell him what is wrong.
hi gasman, hope you get this message as this post is getting old now.
had a chat with the old man about this matter and he put it in a simpler way. if the air side of the expansion vessel is flat then the water in the system will fill the air side too, therefore the pressure gauge will give a low reading (as the same amount of water is now spread over a wider area) so the housholder will then add extra water inadvertantly over pressurising the system, then when the boiler is next used the water will expand but have nowhere to expand to and the pressure will rise triggering the prv.
Hi have alpha 32 combi boiler that keeps firing up every ten or so seconds even when easy stat is off anyone have any answers please ?

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