Water running out of vent pipe when boiler turned on

[monks]

Hi, Please can someone point me in the right direction? I have a central heating system fitted in the 80's. It has a Potterton Profile boiler, a hot water cylinder and two tanks in the loft. One for the heating and one for cold water storage. I extended the system with 5 new radiators and fitted a new standard hot water cylindewr and had to fit a new pump after it gave up the ghost. The old pump was an old blue Myson with no details on it. I bought a Grundfos 15/60. Now when I turn the boiler on I get a stream of water coming out of the vent pipe in the expansion tank. I tried setting the pump to 1 but it still runs out. Is the pump too powerful? Can anyone suggest what may be wrong?

 

[doitmyself]

If it's still pumping over when the pump is on 1 the problem is not the pump.

How far above the water level in the expansion tank is the top of the bend in the vent pipe?
How deep is the water in the expansion tank when it is cold?

 

[monks]

If it's still pumping over when the pump is on 1 the problem is not the pump.

How far above the water level in the expansion tank is the top of the bend in the vent pipe?
How deep is the water in the expansion tank when it is cold?

Hi, Thanks for your time in replying. The bend on the vent is about 12" above the water level. The level doesn't change much. When the boiler heats up I get the same amount of water from the vent except it's hot. Many thanks.

 

[monks]

Hi again, I 've just realised what you meant about the water level in the tank. It was quite high - near to full. I think I can see where you are going with this. Do I need to raise the bend in the vent pipe? I've got about another 2 feet before I hit the roof. Cheers

 

[doitmyself]

Hi again, I 've just realised what you meant about the water level in the tank. It was quite high - near to full. I think I can see where you are going with this. Do I need to raise the bend in the vent pipe? I've got about another 2 feet before I hit the roof. Cheers

The first thing to do is lower the water level in the tank.

Wait until the water is cold then use something to bail out the water a bit at a time until the ball valve opens to let the water in. Tie up the valve as soon as it start to run and check the depth of water in the tank. It should be about an inch above the outlet at the bottom of the tank. If the level is too high, bend the arm of the ball valve down and try again. The important thing is that the valve opens before air can enter the lower outlet, but an inch above is OK.

Now let the tank fill to its normal, cold, level.

When, the system is cold, the water in the vent pipe is at exactly the same level as in the tank, but when the water heats up it rises further in the vent pipe due to the small size of the pipe compared to the surface area of the tank.

Measure the vertical distance between water level and the top of the bend in the vent pipe; it should be more than 450mm. If it's less than this you can get pump over.

 

[monks]

The first thing to do is lower the water level in the tank.

Wait until the water is cold then use something to bail out the water a bit at a time until the ball valve opens to let the water in. Tie up the valve as soon as it start to run and check the depth of water in the tank. It should be about an inch above the outlet at the bottom of the tank. If the level is too high, bend the arm of the ball valve down and try again. The important thing is that the valve opens before air can enter the lower outlet, but an inch above is OK.

Now let the tank fill to its normal, cold, level.

When, the system is cold, the water in the vent pipe is at exactly the same level as in the tank, but when the water heats up it rises further in the vent pipe due to the small size of the pipe compared to the surface area of the tank.

Measure the vertical distance between water level and the top of the bend in the vent pipe; it should be more than 450mm. If it's less than this you can get pump over.

That's great. I'll give it a try tomorrow, it does make sense. I didn't change anything other than what I've already said so I don't know why it suddely decides to overflow. Maybe the pump was quite knackered and didn't have the guts that this one has. Anyway I'll let you know. Thanks once again, you're very kind.

 

[diamondgas]

That's great. I'll give it a try tomorrow, it does make sense. I didn't change anything other than what I've already said so I don't know why it suddely decides to overflow. Maybe the pump was quite knackered and didn't have the guts that this one has. Anyway I'll let you know. Thanks once again, you're very kind.

monks there can be another issue, that being the position of your cold feed and vent pipe relevant to the pump. Also the resistance through the system. If you have a bi-pass fitted you could try adjusting that open a bit more or fitting an automatic one. Folk tend to fit a boat load of TRV's these days that shut off which has an effect on the pump performance and pressures generated! Pumping over usually occurs when there's a large negative 'pull' on the cold feed. The additional water drawn down has only one pace to go which is 'up' the vent! That's my take anyhoo's ...

 

[arran197]

Has the pump been fitted the right way?

 

[armourer]

Or is the system air locked?

 

[IDCHAPPY]

Might be easier to change it to a sealed system if possible, they usually create less hassles.