Expansion tank overflows

Aidan · 25 Apr 2005

Hi, can anyone give me possible reasons for the h/w expansion tank overflowing particularly from cold start up. I have tried the following.
1) Lowered the boiler circulating pump pressure
2) Lowered the hot water cylinder circulating pump pressure
3) Extended the overflow pipe to be about 2.5 feet above the tank.

The system has dual temperature valve controls that independently turn off the heating in the radiators at ground level and first floor level

Any help or advice appreciated

Aidan

fireman22 · 25 Apr 2005

sounds as if you have a blockage or a restriction somewhere. do you mean its pumping over into expasion tank in attic?

Aidan · 25 Apr 2005

fireman22 said:
sounds as if you have a blockage or a restriction somewhere. do you mean its pumping over into expasion tank in attic?

Thats right fireman22, it is pumping over into the expansion tank in the attic. It is at its worst if I have the upstairs radiators turned off using the themperature dial on the wall. I have hard water, do you think that a build up of limescale might be contributing to the problem.

masona · 26 Apr 2005

Have you tried turning the boiler stat down, it maybe water heat expansion from the start up.

Aidan · 26 Apr 2005

masona said:
Have you tried turning the boiler stat down, it maybe water heat expansion from the start up.

I will try that this evening but as far as I know it is pretty low ie.. 60-65. Will let you know the result. Thanks

Aidan · 27 Apr 2005

Aidan said:
masona said:

Have you tried turning the boiler stat down, it maybe water heat expansion from the start up.

Click to expand...

I will try that this evening but as far as I know it is pretty low ie.. 60-65. Will let you know the result. Thanks

This morning I reduced the boiler stat from 68 to 60. I turned on the heating system from cold startup and within about 10 seconds the overflow expansion tank again pushed out about a litre of cold water. The water flows for a few minutes and then eases off. Hope this helps. By the way I reversed the boiler stat back to 68.

Regards
Aidan

ChrisR · 27 Apr 2005

It is not an overflow, it's your VENT pipe. An overflow goes to outside.

Normal expansion of the water will not do it.

Has it always done it?

Is it worse on HW only or CH only or Both?

Usual suspects are bad design of system, exacerbated by scale/ sludge in the heating system.
Limescale is different and only affects tap water circuits which this isn't.
Hot water cylinder and hot tap water pump settings are not relevant.

Heating circuit pump speed may affect it but it still shouldn't happen. The vent pipe should be high enough to stop the water's momentum pushing water out when the pump stops.

What boiler is it and is there a bypass, if so what sort?(Look bypass up!)

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Expansion tank overflows

Similar threads