Hot water venting into Cold Tank

[supersubby]

Hi Guys, can you help me?
I have recently changed all (but one) my radiator valves to TRV types.
As has been (laughingly) summer I haven't had to use the CH.

Now I have started to use the CH I noticed water coming from the overflow, on checking the cold water tank hot water is venting into it (over pumping).
This happens whether its heating the water or the CH.

The header tank is also filing up and the water being drawn into the system.

All the rads have been bled

Any ideas

 

[JohnD]

quite likely a partial sediment blockage.

Did you clean and flush it when you were replacing the valves?

did you add inhibitor when you filled it?

How much mud is in the F&E?

What sort of grime came out when you took the old valves off?

What speed is the pump set to?

How hot are your radiators getting?

What size are the pipes to the radiator?

How do you know it wasn;'t doing the same last year?

Have you adjusted the ball float so the F&E is only a couple of inches deep?

Read no. 20, 47 and any others that look interesting
//www.diynot.com/forums/viewtopic.php?t=37170

A chemical clean is cheap and easy and is always a good start.

 

[supersubby]

Hi John
Thanks for the quick reply

Ran a cleaner through the system for a couple of days then drained it.

I flushed each Rad through with a hose outside

Dont think I added a inhibitor yet

There is a smale amount of rust covered flakes in the F&E tank, although when I drained the system I removed as much of the muck from the F&E tank

The grime that came out of the valves and the rads was black sludge like old engine oil.

Had the pump set to 1 to start off with used to be set to 2 or 3

The rads set to hot with the TRV's get hot enough

15mm pipes to the rads

I know it wasn't doing this last year because I had to replace the ball valve in the cold water tank so I kept a careful eye on the overflow just in case

The Ball valve in the F&E allows the tank to fill to about 3 inches below the overflow.

Hope that gives you the answers, very interested to hear what you think.

Cheers Ian

 

[JohnD]

pump speed?

and adjust the ball so the water is only a couple of inches above the F&E outlet in the side

Measure how high the bend in the vent pipe is, above the F&E water level.

you must add inhibitor at once as it will be rusting fast

Personally I would add X400 again anyway while you puzzle it out. it is difficult to get an old system fully clean. Four weeks is not too long.

If you can afford an extra £100 or so a Magnaclean will astonish you at how much black sludge it pulls out.

As a test, open more rads fully so the circulation is easier, and turn the pump to low speed.

 

[supersubby]

lines 7 and 10 i think

Just looking at the info you directed me to, looks very interesting thanks

 

[JohnD]

thanks, I had missed that. I added some more thoughts. (above)

 

[supersubby]

Did I metion that the water is venting into the cold water tank and this in turn is making the hot water Brown!

Just off to buy some inhibitor now X400

 

[JohnD]

No, I thought you meant it was venting into the F&E (small) tank.

It is generally correct for the Hot Water Cylinder to vent into the Cold Water Storage cistern (large tank of tapwater) if the cylinder overheats, e.g. immersion heater is faulty and it is boiling and the hot tap water rises up.

and for the central heating/boiler circuit to vent into the Feed and Expansion (small)

So I wonder which is the vent that is causing the trouble, and if the vent has been put over the right tank.

Water from the radiators/boiler is not supposed to get into the tap water, since it will be contaminated with rust and chemicals. And tapwater is not supposed to get into teh radiator water, since it causes rusting. One cause can be a fault in the cylinder where the coil has an internal leak, otherwise it would be poor pipework design.

I also wonder what sort of cylinder you have got. i am not familiar with the old primatic cylinder.

Some photos of the tanks and pipes in your loft, and of your hot water cylinder showing the various pipes that go into it, top, sides and bottom, would be very useful.

It is important to know the relative heights (above ground level) of the large and small tanks.

BTW Sentinel X400 is the Cleaning (sediment loosening) chemical. the Inhibitor is sentinel X100. You don't want either of them to get into your tap water. You might have to rig up a hose so any pumping over goes into the F&E.

 

[supersubby]

Thanks John, I will take some photos and post them up.

I bought some X400 and X100 and take on board what you say, as It would just end up being pumped into the cold water tank.

In my simple observation it would seem that water is being drawn from the F&E tank to take up the shortfull of water being over pumped into the cold water tank!, and as you say the 2 systems shouldn't mix as you would get cross contamination.

Can it have been wrong for this long?

I guess so.

 

[supersubby]

John
I cannot post Photos of the CH WH system but there are in my album if thats any good

 

[JohnD]

I can see a vent pipe over the F&E, but not over the cold water tank

Cold tank and F&E Tank

• supersubby
• 2 Oct 2008
• 1

//www.diynot.com/network/DIYnot/albums/67/189

 

[supersubby]

If you look closely at the LHS of the cold water tank you may see the vent.

I lifted it out over the tank to the side and then connected a black hose to vent into the F&E tank.

Try the 2nd image

I will post up a clearer image on my album.

Cheers

 

[supersubby]

New image up now in my album

 

[supersubby]

Temp vent link pipe

• supersubby
• 2 Oct 2008
• 1

Thanks for the photo posting tip

 

[twgas]

can you trace the vent pipes back to the airing cupboard to make sure the vent from the cylinder goes to the big tank and the vent from the heating goes to the small one.

then you need to check to see if you are pumping over, which I suspect you are. As far as I can see the obvious cause would be a partial bockage around the coldfeed/open vent connections.