Grundfos MQ 3-35 0.55kW Boost Pump- has packed in can I still have heat??

[bmitie]

My faithful old Grundfos MQ 3-35 0.55kW Boost Pump has seized up, my own fault and I have to wait a few days for a new one. Same model so should be able to fix it myself. In the meantime I have a closed CH system and occasionally I hear booster come on when heating is on, its only for a brief spurt so I am assuming its topping up CH. But can I have my heating on even though the booster pump is off. The booster pump is for the taps and power showers.

The reason the Grundfos MQ 3-35 0.55kW Boost Pump is gone is that it was allowed cycle when water was switched off, I know I know, I should have unplugged it. I did try for airlock, capacitor and drained pump.

Help

 

[Madrab]

If this is for your taps and shower, then it has no interaction with your CH system. If you hear the pump coming on now and again then it may be you have a leaky tap or a dead leg and the pump is just re-pressurising the system.

 

[bmitie]

Thank you for quick reply. I can relax now. As an aside what does dead leg mean?? The system has been going for 14 years and as I had never used taps without the booster I am shocked at the lack of pressure.

I cant get a plumber to call and fit new pump so I am going to do it myself but the bit that puzzles me on the u tube video is about venting? Mine has a gravity feed so when I open tap it will fill pump or am I missing something.

The vidoe shows as if water is drawing from a well and I can see the logic of venting.

 

[Madrab]

Venting is required depending on how the pipework is orientated. If the pipework rises above the level of the HW cylinder/cold water cistern then air can be trapped at the highest points and needs to be vented otherwise the pump will not run properly or can be damaged.

That being said you do need to prime the pump regardless (run all air out till only water before the pump is run).