Water noise in central heating

[markbb]

Hi I hope somebody can help.

Sorry if I get some wording wrong as I'm not a plumber.

Each time the central heating pump starts in the upstairs cupboard we can hear rushing water noises for a few seconds then it goes and the system is quiet. Sounds like lots of air in the system.

I have read some other topics and tried a few things:

Just before the pump, on the return side, there is a water feed from a small tank in the roof, and an overflow/overpressure pipe.

1, I turned off the water feed to the topup tank in the roof to see if we had a leak. After about 1 week I checked the water level and it had not changed so suspect there is no leak in the system.

2, I put a cup of water under the overflow/over pressure pipe and when the pump starts nothing happens. When the pump goes off there is a single bubble of air pushed out.

3, I have bleed all the radiators many times after the system has been off a while. Only water has come from the radiators, no air.

4, The system is 15 years old and the radiators are hot top and bottom.

Where else could I try to get rid of the air, or where else could it be getting in ?

Any help would be great as it wakes me up when it starts.

 

[seco services]

Poss the cold feed is blocked/restricted.

 

[markbb]

Thanks, Good point. Would this be a good test ?

I will turn off isolating values each side of pump, remove the pump and open the top valve to be sure lots of water comes out into a bucket and check the tank is filling.

 

[seco services]

You can isolate the ball valve in the f/e tank, open a draincock see if the tank level drops.
Run a magnet over the cold feed pipe near where it joins the system see if it sticks.

 

[markbb]

OK, Found a drain point downstairs under a radiator, connected some hose to it and opened the valve. Warn water started flowing, so I run into the roof space and could see the filler tank only half full and filling from the ball valve.

I guess this means the cold water feed is working.

Anything else to try to get rid of the air ?

 

[45yearsagasman]

View media item 39013This may help you to decide if you have a blockage near the feed and vent area. Not 100% as the blockage may not be magnetic.

 

[danny1985]

Have you bled air out of the pump? switch pump to highest setting. Turn central heating only on.. If there is a bypass just after the pump close it fully. Shut all radiators apart from one. bleed the radiator then shut off. Open another and bleed then shut off repeat this until all radiators are vented. By only having one radiator open each time with the system on, this method increases the pressure which creates a better chance of getting all the air out. Once you have vented them all, open up all radiators and the bypass(If there is one) and test for the noise.

 

[danny1985]

Make sure you turn the heating off when switching radiators as with all radiator switched off at once the boiler will over heat..

 

[markbb]

After bleeding the pump and radiators should the bypass valve be open closed or something in the middle and how to find the middle point ?

 

[danny1985]

It only has to be open slightly. If you open it to much your radiators might not get as hot. let me know how you get on?

 

[markbb]

OK, an update and thanks for all your help.

The noise was air bubbles trapped in the pump that I could not get rid of permanently no matter how much bleeding I did. It would go then come back. It would move around the system then settle in the pump. The radiators acted like speakers transmitting the sound around so it might have been very small but made a great noise.

So... I change the cheap pump to a Grundfos pump, ran the system with x400 in for 1 week, flushed a few times, then finally drained fully and added x100. Then bled as mentioned above and now there is no noise and all is working great.

Not sure where the air bubbles kept coming from, maybe the cheaper pump, but at least its fixed.

Thanks for all the comments and help.

 

[plumbplumb]

It's advisable to set your pump speed to match the system.
Try it on 1 first if there is no noise from the boiler and your radiators heat up ok then leave it on this if not try 2 before setting it to the maximum.

The pumps job is to overcome the resistance that's created by the central heating system.
Setting the pump too high may create problems down the line and maybe just overcompensating for issues in the system I.e incorrect configuration of the cold feed and vent/pipework restrictions etc.

 

[markbb]

Thanks for that.

The pump was on full for a while while clearing all air, now that its all bled its quite on all 3 settings, but its now running on 1 and quiet and warm.