Combi or standard boiler

I would make an educated guess that the flow rate discrepancy between kitchen tap and all other cold water outlets is they are tank fed from the loft hence the dramatic difference in flow rate, now to your primary question: Pros of a Combination boiler: 1. Not paying to store hot water 2. Frees up space where your hot water cylinder once was (if installed in a different location) Cons of a Combination boiler: 1. Labour & material cost higher as this type of boiler requires a mains cold water feed and a hot water pipework outlet 2. If boiler completely fails then no heating or hot water (unless you have an electric shower) 3. Low mains cold water pressure can bean issue but you have stated that you have 13l/pm mains cold water which is fine 4. More parts in a Combi boiler as opposed to a Regular/Heat only boiler so the likely-hood of component failure is higher 5. Combi boilers have limited hot water flow rate regardless of how good your mains cold water pressure is so if you have more then one bathroom that the boiler serves then expect the furthest one away to have poorer flow rate NB: As you will see the 'Cons' far out way the 'Pro's' but depending on the type of property you have and other matters for consideration you can now make an informed decision Foot note: I have just moved in to a 3 bedroom house with two bathrooms, I removed the Combi boiler and replaced it for a System boiler and 200Ltr Un-vented cylinder so when both bathrooms are being used simultaneously each person has a plentiful supply of hot water but this type of system is also good mains water pressure reliant !

Check cold water main is lead or not, if lead change to blue plastic with bigger diameter, put a mains booster pump on incoming mains or get a combi boiler that works fine on 14 litre per minute if that's what you have, check manufacturer installation guide

You may simply want to boost the flow and pressure of a shower or tap supplied with hot water from a combination boiler or protect the flow and pressure when someone opening a tap elsewhere in your home causes your shower to fluctuate. In more serious cases the combination boiler will shut down and run cold. There are two reasons a Combi Boiler will shut down and they are:- 1.0 Insufficient hot water flow from the Combination boiler 2.0 Insufficient pressure before the Combination Boiler when water is demanded. The Shower Power Booster will solve all of these problems and it is legal to fit one before or after a Combination Boiler. It is perfectly safe to use ShowerPowerBoosters boost water before and after a Combination Boiler

I agree entirely with what Boiler Homecare has said, however please oh please get the difference between water pressure & flow rate. Also while I'm in the mood for a rant, do you realise the critical differences between a basin & a sink ? People calling basins sinks drives me f***ing mad. Likewise, you can have high water pressure yet suffer from poor flow rate. These differences are important & make a crucial difference in understanding of a problem. Take BH's advice & I hope you make a wise decision. If in any doubt then contact a decent plumber.