Constant bleeding of radiators

[grahamw01]

Can anyone help me please. Since moving into my house (1900 victorian end terrace) I have had constant problems with my central heating. It's an old style stored hot water cylinder with CH expansion tank above it in the airing cupboard and cold water storage above that (still in airing cupboard, which is in the bathroom).
I've replaced the pump, which lies under the bath before the 3-way value. The boiler is downstairs in the kitchen. I've also change the 8mm microbore copper piping which fed the rads downstairs with 15mm plastic piping. When I switch on the CH, the rads upstairs get nice and hot but the 3 rads downstairs get fairly warm. The rad in the bathroom, which is the first one on the feed and return pipes always seems to get full of air, after about 15 minutes of the CH being on it requires a bleed.

Can any help please

Also would it be a good idea to move my cold water storage tank to the loft, would that increase the presure in my very old mixer shower

 

[EliteHeat]

Did you put the pump in the right way around? it sounds like it is sucking air into the system. Which way is the arrow pointing in relation to the 3PV?

Increasing the height of your cold water cistern should increase the pressure and flow rate to your outlets.

 

[grahamw01]

Thanks for the reply EliteHeat, I made sure the pump is in the right way (at least I think) the arrow points towards the 3pv, which I assume represented the flow of the water.

Would putting the cold water tank in the loft make mush a difference though, I mean it will only be about 3-4 foot higher

 

[EliteHeat]

Ok the first thing you need to do is find out where air is entering the system. Since it is an open vented one, the prime suspect must be the vent itself. If you can access it, try holding a glass of water under it so the vent is below the waterline, run the CH and see if it sucks the water in.

Shoud this be the case then trace the cold feed and open vent pipes on the system. They should be within 6" of each other and arranged so your system is under positive pressure.

As for your cold water tank. For every metre you raise it, you increase the water pressure by about 1.5lbs per sq inch. It's really up to you to decide whether it is worth the effort. You may decide that putting a pump on will get you a better return.

 

[grahamw01]

If I remember right, a 22mm pipe comes from the boiler and just before it goes into the pump, it splits off to a 15mm pipe, this 15mm pipe is what I think is the expansion pipe, it basically sits over the CH expansion tank. Is this the vent your talking about?

Would the pump go immediatly after the pipe come out the top of the hot water tank?

Thanks for your help

 

[EliteHeat]

The 15mm pipe is probably the cold feed from the header tank. You should see a 22mm pipe immediately before or after it, teeing into the same pipe from the boiler - this will be the expansion/vent pipe. You need to locate thisl.

 

[grahamw01]

I don't think it is the cold feed, no water can get into the open end. It just loops over the CH expansion tank. Also it splits off the 22mm pipe that carries the hot water just before the pump.

The only thing after the pump is the 3 port value, one way goes into the hot water tank, which obviously heats the hot water and the other way is the feed to the rads, I've followed it and it goes to the first rad, which is in the bathroom.

I've located the return from the rads and on its way back to the boiler, a 15mm pipe from the CH expansion tank joins onto it (which I assume is the feed) and then at another point, the other end of the coil in the hot water tank joins it, it then runs back to the boiler

Thanks again

 

[EliteHeat]

Can you try the glass of water trick?

 

[grahamw01]

I will, do I hold the glass under the pipe that loops over the CH expansion tank

Thanks