Inline Mains booster pumps (combi system)

[oldbutnotdead]

Good odds the kitchen tap is fed with skinny flexis and possibly a restrictor nozzle type thing. The boiler may have a restrictor in it (some brands I understand have a max flow rate of x but by default are derated either in software or hardware to x - 20% or so). The pressure/flow difference between bath tap and the rest of the house may just be down to a straight pipe run to the bath Vs a pile of elbows in the runs to everywhere else.
Bonus if you've got access where the MDPE comes in- yes my thought was to run a temp supply to the cold feed of the boiler- ideal if you can tee in just above the mdpe- and see if better mains supply gives you better dhw output.

 

[hotspot007]

The kitchen tap doesn't have flexi pipes.. Its just 15mm copper up to the connection of the tap. It does have a aerator / restrictor in the nozzle - I tried removing that and it gives exact same flow. My boiler does have a flow restrictor in - which is 11 litres / min I'm told.
There's no where to tap off the blue pipe.. Its straight in - and into my meter the outlet of the meter is directly into an elbow and into the wall

 

[oldbutnotdead]

Ahh boo, oh well. Are there isolator valves in any of the runs to the taps- the cheap ones are very small bore. How's access to the cold feed to the bath?

 

[hotspot007]

There are isolator valves to the kitchen sink taps but there was none to my 3 basins - at which I have just added isolators and check valves to the hot (as I thought my mixer taps were passing)
Access to the bath cold is a no go. They come up through a drilled hole in the tongue and groove flooring. I'd have to cut away the flooring.
I have British gas coming back out in a couple of weeks. Hopefully they will change my plate heat exchanger - and I get back to 9litres a min. I'll report back.
As for the booster pump. I'm worried now - that if I do have a flow restrictor / pressure reducer hidden somewhere... Then the pump will do nothing as it will be pumping up to that

 

[Madrab]

I have a greenstar 30si.... Think max flow is 12litres a min

If I remember rightly this boiler is flow limited (not sure what to, would need to check) though it is rated @ 14.3L/Min @ 30Deg rise though that would need a min dynamic pressure to attain that, to overcome the resistance in the plate, it's usually around 2bar.

 

[hotspot007]

You are right, 2 bar minimum to achieve max flow rate.
Max flow is 10.8 +/- 15% - so @ 2bar I should get 9litres a min. Which is what is on my commissioning paperwork for the house. (2 bar/9litres a min 50degree rise taken as 7degree cold water inlet temp - 57 at all outlets )
I have 2 bar still and 9 litres from my cold tap - but 6litres/min hot.
This surely enough to make the boiler cycle on and off whilst I'm showering (observed the boiler flame out and back on... Repeatedly)
So this would point at a furred up hex?
I know I'm on the minimum - but everything always worked at the minimum, so I guess when you work at the minimum pressure you have a lot smaller operating window for my size boiler to keep running with flame rather than cycle.