Replacement for Myson Unit 5 ch pump

[Invisible Man]

Pump has been a bit weak ever since we bought the house. Now getting noisier and less effective.

Ideas for a replacement please.

House is 3 bed detached reasonably well insulated in Essex. 2 storeys about 500 sq ft each.

All pumped system. Boiler is a 24HXI, usual 25mm pipes to ordinary rads.

We get some horrible airlocks so something that is easily bled and with a bit of oomph would be good.

As usual it is in a position where it would be difficult to change the pipework. Prefer one that would fit the same as the Myson.

TIA for any advice.

[cynic]

Why do you suffer repeated airlocks? Once the system is settled you should not get any.

[Invisible Man]

Just whenever I do anything. Eg. turn off radiator, drain rad down and remove it to decorate. Turn off system, reconnect rad. open 1 valve and allow air to escape from bleed valve until water appears. Turn system back on and airlock causes boiler to overheat and cut out. Never had a place like it. We have done a lot to this house in the 3.5 years we have been here and it is a real pain.

[cynic]

That sounds as though you have a more fundamental problem which needs sorting out before you go throwing money at replacing the pump. For a start do you have an open vented or sealed system? if open vented does the pump "push" the water around from the neutral point or does it "pull" it back from the rads? If sealed does the pressure remain above about 0-8 bar when cold? Do you have any kind of corrosion inhibitor in the water? Just a slight modification to suggest to your refilling procedure after refitting a radiator - when in place and tightened up (and pump switched off) open the rad vent and one of the rad valves for a few seconds, close the rad valve and open the other so you are expelling air from both the inlet and outlet connections as you refill. The amount of air in one connection should not cause the problems you describe but it does at least ensure you clear both.

[Invisible Man]

Thanks for the idea on clearing rads from both ends - one at a time.

System is open vented, pump pushes water from boiler to 3 way valve to rads and hw cylinder.

Fernox in the system. System is pretty clean. The system does not collect air once it is all out. No reason to believe air is sucked from the overflow. the pump is getting noisy and the flow rate is not as great as I would like.

[cynic]

te:

Ok - it sounded as though you had a continuous air problem but this is not the case. My reccomendation would be to fit a Grundfoss pump and your local plumb centre or other stockist will have a chart to say which model would have the right performance. If the replacement is a different connection you should make the modification as it will be a once only exercise

[Invisible Man]

Thanks for your help. The noise and vibration from the old pump woke me up this morning. I could no doubt cut the vibration but previous experience suggests it is not going to last forever so I will do it when it suits me rather than when it finally stops at an inconvenient moment.

[Invisible Man]

Fitted a Grunfos Alpha+ 15-50. Quietest pump I have ever heard (if I put my ear to it). Also took the opportunity to siphon some of the silt out of the Myson Aerjec. Googling suggests they are prone to getting blocked.