Help needed to understand the purpose of another pipe and valve for expansion tank

[papaya]

Evening guys,

I'm slowly learning how my central heating system works and I would like to ask for your help to understand the purpose of the pipe and valve used with my expansion tank as I can't see the point there :disappointed:


I understand that the white pipe (bended) is overflow and the one with green insulation is the cold feed to the F+E and the other high paper clip type pipe is the expansion pipe for extra protection as all water through it will eventually drop back to the tank BUT I don't seem to understand the one on the right with the valve (circled).



The reason is that this valve controls the water from expansion tank to flow with the hot water from the left through the heater pump. If I turn it off, just the hot water from left will come through to the pump but if I turn it on, it will mix with the hot water comes from left and results in only cold water come through the pump. So what's the purpose of that and should I leave it on or off? I know it sounds stupid but I can't figure out why...


In addition, I would also like to know how could I check if the copper coil in my water cylinder has pinholes?

Many thanks! :blush5:

 

[Mike Jackson]

So does it mean the cold feed is used in conjunction with TRVs of radiators to control temperature?

No. It just keeps the system full of water.

 

[papaya]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

I was trying to figure out why my radiators are cold when the CH is on as when I touched microbores connected to primary flow, they were cold. I traced all pipes up to my loft and eventually discovered that, so I thought it could be a problem as hot water mixes up with cold water. So like you said, regarding the water ingress, what will be the best solution then? Sorry my knowledge of plumbing is poor.

 

[papaya]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

No. It just keeps the system full of water.

I see, thanks!

 

[Crinkmeister]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

I was trying to figure out why my radiators are cold when the CH is on as when I touched microbores connected to primary flow, they were cold. I traced all pipes up to my loft and eventually discovered that, so I thought it could be a problem as hot water mixes up with cold water. So like you said, regarding the water ingress, what will be the best solution then? Sorry my knowledge of plumbing is poor.

I don't think the person who installed that system knew much either!

 

[thompsonbrown]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

pipe is cold feed to central heating system if you don't think you need it try filling your heating system after a rad swap. also its in the wrong place to close to the pump and should be tee'd in from underneath

 

[Mike Jackson]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

Doesn't have to be teed in from underneath (in fact looping underneath means there is more likelihood of the cold feed blocking) and no issue with the proximity to the pump. There may be issues with the open vent as I can't see exactly where it is connected and it has been raised very high, presumably to resolve a pumping over issue. I'm assuming that the pump is pumping left to right in the picture.

 

[thompsonbrown]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

i would check out the cold feed best practice guide, i was always taught that by feeding the heating system from underneath that it would have less chance of drawing air from the f&e tank also less chance of dragging air into the system when filling do you have any evidence of this changing since 1986 i would really like to know if it has but you are correct about the positioning of the pipe.

 

[papaya]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

Doesn't have to be teed in from underneath (in fact looping underneath means there is more likelihood of the cold feed blocking) and no issue with the proximity to the pump. There may be issues with the open vent as I can't see exactly where it is connected and it has been raised very high, presumably to resolve a pumping over issue. I'm assuming that the pump is pumping left to right in the picture.

Mike, you are right the pump is pumping left to right as this can be identified by touching the pipe when the valve is open as cold water will go thru from left to right.

 

[diamondgas]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

I was trying to figure out why my radiators are cold when the CH is on as when I touched microbores connected to primary flow, they were cold. I traced all pipes up to my loft and eventually discovered that, so I thought it could be a problem as hot water mixes up with cold water. So like you said, regarding the water ingress, what will be the best solution then? Sorry my knowledge of plumbing is poor.

With the limited knowledge you have I'd advise you get someone in However in the mean time, did all your radiators go off at the same time or was it a gradual reduction? What sort of boiler do you have? Room thermostat fitted? Diverter valve fitted?

Realy need to know a bit more about your system design to give you a better idea of what the possible issues may be IMO

 

[papaya]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

With the limited knowledge you have I'd advise you get someone in However in the mean time, did all your radiators go off at the same time or was it a gradual reduction? What sort of boiler do you have? Room thermostat fitted? Diverter valve fitted?

Realy need to know a bit more about your system design to give you a better idea of what the possible issues may be IMO

Thanks diamondgas. I have a Worcester Greenstar 18 Ri, my central heating system is vented (the common one before 2000). For my radiators, the problem is that they take ages to heat up and usually they just stay cold. I have a thermostat in the corridor and have a 3 port motorised diverter valve. I have asked my plumber to check it today and he said my cylinder keeps generating air to the whole system because of damages in the coil so it cannot be properly solved unless the cylinder is replaced. He has tried to release air lock and now we have lukewarm water - better than no hot water at all.

Now I have a question, if I turn off all radiators, turn off the control and turn off the cold feed for expansion so that cut off the radiator circulation from the system and just leave the hot water circulation in the system. In that case, will my hot water be back normal?

Thanks again,

 

[Dannypipe]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

Don't cut off the cold feed to the feed and expansion tank. As said, there shouldn't be a valve there anyway.

If the coil has pin holes in it then that could explain the dirty water at your taps.

However it could be other factors.

If your feed and expansion tank starts to over fill and the overflow runs, then you have pin holes in the coil. The water will try (as said) to balance at the tanks.

However deal with one issue at a time. Your radiators are all cold. Correct?

You're hot water isnt getting hot either?

Have you checked the pump?

 

[helpsy]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

Cold feed 15 mm

 

[Dannypipe]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

Cold feed 15 mm

Well Helpsy, that was insightful. Helpful even. !!!

Anyway, i'm off to bed. Good luck with your endevours OP. I reckon you may need a second opinion, maybe get someone from the forum to take a look. Your man may have got misguided. Happens to us all at times.

 

[helpsy]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

Wondering if the neutral point is blocked as vent pipe excessively high (450 above water level) pumping over

 

[Whyme]

Re: Help needed to understand the purpose of another pipe and valve for expansion tan

like i and many said dont turn off the valve. best bet is get a plumber round and give you a real life hands on diagnosis because theres only so much can be said over tinternet