Combi boiler, disconnecting booster pump?

Repairman77

Hi, we have recently swapped over from a back boiler, tank, booster pump system to a Combi Boiler for several reasons.


British Gas sent a contractor to install it all and it works well.
However I did point out to them that there was a shower/bath booster pump in the system which I disconnected the mains supply to.


We noticed that on the new combi system that the bath took a lot longer to fill up. Checking under the bath I found that they were letting the cold and hot supplies to the bath run through the disconnected pump. I assume that as the pump has multi-fin impellers this would slow the flow somewhat.
I had assumed that the engineer would have bypassed the pump altogether.

Any plumbers or gas engineers on here; how would you have connected it? Do you think the engineer simply forgot or saw a reasonable flow so just left it?


Thanks in advice.

nofoollikeold

Probably forgot. It ought to be removed and replaced with two lengths of pipe.

Combi's do tend to take longer to fill a bath than tank fed systems. The total flow rate is restricted to that of your incoming mains, whereas as stored water can flow as fast as the head of pressure and pipe resistance will allow. Removing the pump is unlikely to get you back to your earlier filling times.

Repairman77

Thanks for the reply; yes I didn't think I'd get the same as the pump fed system but wasn't sure how much pressure I was loosing by it going through the pump. Any improvement would be welcome and wonder if it was being lazy not rerouting it direct? I'll remind them; no point in me having to do it if it should have been done.

Owain_Moneysaver

Also, the flow through a combi is limited by the power of the boiler and the rise in temperature required. E.g. a 30 kW boiler will give approx 12.4 litre/min for 35C rise in temp.

You'll notice that especially in winter when incoming water temperature drops to almost 0C.