feed and expansion tank backfilling

[williams215]

hi all. right ive had this once before and cured it with fitting a new cylinder. basically my mate asked me round to stop his f + e tank from overflowing, changed ballvalve as is 90% the problem/cause, but he phoned me up a few days later saying it was overflowing again. this to me then pointed to the cylinder coil being split?? changed cylinder and still have the same problem???? after a few hours the f + e will overflow again...

system is layed out correctly, vent-cold feed-pump . been looking over peoples past experiences with this, and have seen some instances with pipework being blocked on the vent/cold feed, if so how would that cause the f + e to overflow??? also was thinking of emptying the F+E and telling them to not use the boiler at all, all day to see what happens, and also shut off the cylinder and empty F+E again for a day to see what happens....

any help appreciated as im scratching my head......

 

[kozak1968]

Have you got the heating and hot water vent over the correct tanks and not crossed?

 

[buckley plumb]

is the vent pipe 450mm above water level.also in the loft whick cistern is the lowest htg or cold water cistern

 

[williams215]

the f+E is lowest, will double check the heating vent for 450mm. and the vents are not crossed....

is the vent pipe 450mm above water level.also in the loft whick cistern is the lowest htg or cold water cistern

 

[JeffD]

What's it like when running system if you've got a blockage on heating side and it can't circulate properly they normally start banging abit on open vent systems

 

[buckley plumb]

seen it where the cold water cistern is the lowewest and this overflows due to unbalanced passing mixer tap or shower valve - cold forcing up the hot but this is eliminated with your htg cistern being the lowest

 

[williams215]

heating system seems fine, flow and return to cylinder heated up as it should and didnt seem to not circulate?? got to admit the system is an old microbore system???

 

[buckley plumb]

is it filling from feed or flowing out of the vent when the htg is on . could drian cold water cistern and isolate feed to it to eliminate that.

 

[JeffD]

What's the radiators like at getting hot, is it coming over expansion or coming through cold feed when overflowing

 

[williams215]

coming up through the cold feed, takes a few hours after setting the f + e to the right level. even when heating/hot water is off over night it will continue to overflow all night long.......

 

[buckley plumb]

drain cold water cistern and isolate to eliminate that for a night to see if it still overflows.

 

[williams215]

will do and post results cheers

 

[JeffD]

Is it fully pumped heating system

 

[williams215]

yes jeff

 

[Reg Man]

Quote> blocked on the vent/cold feed, if so how would that cause the f + e to overflow???<Quote. If the cold feed was blocked, the system can no longer expand up the cold feed to the f&E so will dump water over the open vent.

 

[JeffD]

If there's def no blockages then there's a back feed problem or something on that route, how long has it been doing it before you changed the cylinder. If the system is really old it won't of been doing it all it's life,

 

[williams215]

right. basically ive fitted a gatevalve lockshield to the return and isolated the flow and return at the coil (2 port shut off and lockshield gatevalve shut off) so far no overflowing last night, tonight im going to open the coil up and see what happens....