Please help me - air near my central heating pump

[Robert Eadie]

Hi, New to this thread, as we are just beginning to experience a similar problem, over past 6 months. When boiler is on HW only, lots of gurgling like air around the system. Less obvious when on CH. We have a single 22mm feed and vent to the system, just past the pump. I've checked the header tank in the loft which is half full, and pushing the ballcock down makes water flow in. Switching the (rather old) Grundfoss pump up to max just increases the gurgling, but doesn't seem to purge it. Can air be dragged into the system somehow? Do I need to investigate a possible blockage in the feed/vent pipe, and has anyone decided the best/easiest way to do this?

 

[Stigster]

The first thing to try is bleeding the pump.There is a slotted screw on the front of the pump which can be unscrewed slightly (no need to remove completely) to let our out. A small amount of water along with bubbles/air will come out of that bleed screw and you will need a small container to catch the water. The screw is standard thread and undoes anti-clockwise. When no more air issues from the port, nip the screw up again, just until no more water comes out, no need to use too much force on tightening, just until it seals again. You can do this with the system running.

Once you've done that we will need to hear back from you as it will either cure the problem or if not we can advise further but that is the first step for now.

 

[Aire]

The problems been happening over the last 6 month's, in that time are you noticing it getting worse? Your tank in the loft is full but have you tried bleeding radiators or draining a little water off to see if the water level in the tank lowers and refills?

 

[townfanjon]

When you bleed a rad , do you get air out ? If you do does it smell ?

 

[chris watkins]

Can air be dragged into the system somehow? Do I need to investigate a possible blockage in the feed/vent pipe, and has anyone decided the best/easiest way to do this?

Yes, air can be dragged in either from the vent or from a small leak in the negative part of the system.
A simple way to find out if air is being drawn down the vent is to hold a small cup of water under the open end of the Safety Open Vent Pipe in the F&E cistern when the system is off, then get someone to turn on the system. watch the water level if the level drops there is suction & air could be getting in, if the water level rises this could indicate "pumping over" another way air could enter the system.
My concern is the combined feed & vent being after the pump this is no correct as the system will be almost completely under negative pressure & susceptible to air being drawn in without any signs of water leakage.

 

[John.g]

If the pump is on the flow side pumping away from the boiler then yes, the combined vent&feed should be before the pump, some systems, like my own, have the pump on the return immediately before the boiler and the vent is a continuation of the T off from the cylinder coil (flow side) with the feed teed in where the vent passes up past the feed&expansion tank, my attic bedroom rad certainly runs under negative pressure and I does require very infrequent venting with the circ pump off, a neighbour had a identical system which started to get noisy like the op's, eventually cured by replacing the pump isolation valves fiber washers with rubber ones, it probably must have been pulling air in on the suction side even though there was no visible signs of leakage anywhere around this area.