Bubbling noise

[michael]

Hi, I have problem with my heating system. The system has a single pump system with 2 zone valves one for hot water cylinder and one for heating.

The problem is when the valve for hot water is open which feeds the cylinder, there is bubbling noise coming from the overflow pipe to the small expansion tank. When the heating only is open its seems fine. Only when the hot water is on there is bubbling noise. The pump is set to speed III, if i turn it to II the bubbling noise is not there, but the rads don't heat up.

My cylinder, and both zone valves are in the loft. The cold water feeder from the small tank in connected to the return from the cylinder.

Does anyone know what the problem might be.

Michael

[Dave Plowman (News)]

Have you looked at it? If water (and or 'steam') is coming out of the pipe it's called pumping over. Which is not 'a good thing'

Have the rads been balanced? If all the lockshields are wide open the pump might well need to run flat out to circulate the water. Balancing them should allow it to be turned down. Details on balancing in the FAQ.

[michael]

=A0 London SW

When the heating is on (only) and not the hot water its fine all rads get hot, its only when the hot water is on either with or without heating does bubbles appear and air goes in the system from the overflow vent.

[TheScullster]

"michael" wrote

Hi Michael Have you bled and re-bled all the rads and any other bleed points on the system? My system tends to be noisier at start up when hot water only is being heated. Once all the air is eradicated (say after a drain down), the system quietens down. If your zone valves are high in the system and close to the vent and/or fill points (this is pretty standard with pump and valves in airing cupboard), then they are more prone to magnetite deposits. If the system is older - say 10 years plus - then this may be an issue. The deposits reduce the bore of the pipe and valves which results in higher water velocities locally (hence perhaps bubbling). The only way to check will be to drain down, partially, and remove/inspect valve and pipe work.

As others have said, if you are seeing water pumping over the vent into the header tank, then this needs to be resolved. Test the system in all modes to make sure this is not occurring.

Not sure why you would need speed 3 to get rads to work - is it a micro or small bore system?

Phil

[Dave Liquorice]

Sounds as if the pump is working to hard and drawing air down the vent pipe when in HW only. The physical layout of pipes/pumps and vent/feed connections are important. I think you'd find the recomendations on the Grunfoss site.

You say that if you use II that doesn't happen but the rads don't get hot. Is that with HW and CH demand or just CH? I'd look at the CH circuit as Mr Plowman suggests and make sure the system is balanced and doesn't have any air locks or rads full of air.

[michael]

Hi Phil, Its a 15mm system. The plumber re-located the vent after the pump but before the heater zone value. It now goes down by 12" then U turns up to the expansion tank. (Before, the vent was before the pump on the same level as the inlet to the hot water cylinder) Now the bubbling noise is gone. Now when heating and hot water is one all in fine. But when the hot water only is on there seems to be a problem of air in the system, as the boiler turns off after a short while and the temp goes up to 75c which I have seen when there is air in the pipes.

I should say the hot water cylinder, the two zone valves, and the pump are all located in the loft. The boiler is in the kitchen.

Michael.

[NT]

sounds to me like air in the radiator circuit. Turn pump speed down first, as you'll never resolve it without doing that, then bleed all rads. I'm no expert on this stuff though.

NT