Air in my system

sausagehead

Hi, I'm having to bleed my bathroom towel radiator every few days, so there's air getting into the system and my question is .....what would be the most common reason for air entering the system?


Gravity feed oil central heating
water pump set at #1
used to be at #2 but i was getting noise from the pump which seems to have gone away when set to #1

thanks

shane0007

Most common is a system leak or continuos pitching into the feed & expansion tank.

sausagehead

whats that about pitching?

shane0007

You said you have a gravity fed system. In your attic, there will be a feed & expansion tank (the little tank). This will have a hockey stick shaped pipe over the top of it.
If the water level is too high in the tank, when the system heats up, it can pitch water from this pipe into the tank, thus re-oxygenating the system. This can only be checked when the system is on & upto temperature.
Another causes for pitching are a poorly designed system, too much water in the cistern, incorrect location of the circulating pump, a blockage, valve on the f & e pipe turned off, non-return valve seized, system sludge, etc.

Place to start is to look at the vent pipe when system it is on & hot.
Next then, when system is cold, tie up the float valve in the cistern, mark the water level or measure from the bottom (it should be 100mm deep when cold). Leave over night or for 24 hours & re-measure the level, not forgetting to untie the float valve.

If the level is too high, do NOT bend the float valve arm whilst it is in the cistern. Turn off the water, remove the split pin, remove the arm & bend over your knee.

sausagehead

Thanks for all that shane!
would i be right in saying if i had a system leak i would get a continuous drip into the expansion tank to make up for the water loss? or is that not necessarily always the case!

shane0007

Not always the case. It may not be continuous. A weap would be much slower at leaking. It may also only happen when the joint that is leaking expands/contracts from heat & the expansion of the system will hold the float valve closed. It would only add water when the system cooled.
Air testing is best with a compressor but a lot of self tests you can do before you get to that stage.
Most common identifiable leaks are the auto air vents & the slot type pump valves either side of the circulating pump.

corkgsxr

A wrongly placed auto air vent will draw in air too. Close them up

Dtp1979

shane0007 wrote: »

You said you have a gravity fed system. In your attic, there will be a feed & expansion tank (the little tank). This will have a hockey stick shaped pipe over the top of it.
If the water level is too high in the tank, when the system heats up, it can pitch water from this pipe into the tank, thus re-oxygenating the system. This can only be checked when the system is on & upto temperature.
Another causes for pitching are a poorly designed system, too much water in the cistern, incorrect location of the circulating pump, a blockage, valve on the f & e pipe turned off, non-return valve seized, system sludge, etc.

Place to start is to look at the vent pipe when system it is on & hot.
Next then, when system is cold, tie up the float valve in the cistern, mark the water level or measure from the bottom (it should be 100mm deep when cold). Leave over night or for 24 hours & re-measure the level, not forgetting to untie the float valve.

If the level is too high, do NOT bend the float valve arm whilst it is in the cistern. Turn off the water, remove the split pin, remove the arm & bend over your knee.

Ah I love when the float arm snaps trying to bend it and it's 5.30 on a Friday!

sparksfly

Dtp1979 wrote: »

Ah I love when the float arm snaps trying to bend it and it's 5.30 on a Friday!

Yep, a knitting needle and some hose clips repaired mine till Monday morning.

corkgsxr

Dtp1979 wrote: »

Ah I love when the float arm snaps trying to bend it and it's 5.30 on a Friday!

I always carry a spare brass ballcock. Id never bend a old one its always a 50/50 risk.

I had one where I had to drain the main water tank. Turned off water, drained it down. Changed valves. Back on. Popped up to check all ok and arm had snapped off.

Dtp1979

One time I pulled back some fibreglass from a Galv tank and out sprayed water. Really awkward attic. Panic set in. I went to tie up the ballcock to drain tank and it snapped. Then I realised no mains shut off valve to the house. Turned on kitchen sink tap and it took the pressure away thank god

sausagehead

So.... i measured the water level when cold and its sitting at 11.5 cm,
there was no dripping from the valve when i was there for 45mins.
i.ve tied the float and now with the heating on a few hours, the water level has raised to 14cm, the vent pipe which comes down into the tank maybe 2" is nowhere near the raised water level
there is a overflow pipe which goes into the raised water level but not when system is cold!
will check tomorrow to see if theres any water loss when i untie the float!

shane0007

sausagehead wrote: »

there is a overflow pipe which goes into the raised water level but not when system is cold!
will check tomorrow to see if theres any water loss when i untie the float!

If the water level when system is hot is reaching the overflow outlet, then the outlet is too low. This is your problem. You will need to disconnect the overflow pipe, blank the outlet & fit a new one 25mm from the top of the tank.
Where is the overflow pipe going to? Hopefully not into your cold water storage tank! It should be going out to your soffit, terminated in a conspicuous location.

sausagehead

ok thought that when i seen it!
it goes into the water about 1cm or less, i could cut a bit off, it must be about 4" long it goes out of the tank and the same length again down the outside of tank, then away outside!

shane0007

It would depend on the expansion of the system.
Where is it overflowing to?

sausagehead

the overflow pipe goes out the side of the house!

i'm sure if the water level was brought down 15mm to 10cm it would not reach the overflow pipe,would that be better than altering the overflow pipe?

shane0007

It would depend on the temperature of the system & therefore the expansion.
15mm may or may not do. It's a bit fine.

Moving the pipe is a very small job. Only a blank cap (372) & tank connector (350).

sausagehead

IMG_20140125_210244.jpg heres a picture

shane0007

No that's fine, it not the outlet point in the water. Back to square one!

sausagehead

****e!!