So I notice my plumber(s) has used isolation valves which are NOT full bore on my plumbing (See pics).

Whilst I appreciate that taps commonly have a reduced bore within them, I don't really see why these reduced bore valves should be used given they will reduce flow rates, and no doubt there are others placed elsewhere to act as service valves but are flow restricting. It also means my previous measurements of internal flow rates are invalid because plumber(s) are deliberately choking off flow.

I notice when these things are sold it is not made clear that they have reduced bore. The cost of a full bore valve appears to be around £3.50 and a restricted bore one £1.30. The difference is what many people would call insignificant - certainly compared to labour costs.

Is it totally unreasonable to ask for these to be replaced ?

Is there a way to tell the two apart by looking at the valve (while full bore tend to have a lever, the levers are of course removable) ?

Edited Sunday at 14:531 day by Spinny

If you are all on mains pressure the restriction isn't significant - if you are on gravity feed then full bore isolators are the only option as the narrow bore isolators really impact flow.

Thanks marshian, however the words 'isn't significant' is not something I greatly trust coming from most plumbers given the flow issues experienced on my new mains system. From my perspective professionals should not be fitting sub-standard components to systems when the full standard is available for pennies more. The core purpose of a plumbing system is to deliver water flow, restrictions should be avoided not added for no good reason. Plumbers seem to have a tendency to claim every component of a system 'makes no significant difference' then run a mile when the overall system disappoints.

If this is to taps, the taps have restricted flow anyway, so these will make very little or likely no difference.

If they are in a heat pump heating system, that's a different story.

6 hours ago, Spinny said:

Thanks marshian, however the words 'isn't significant' is not something I greatly trust coming from most plumbers given the flow issues experienced on my new mains system. From my perspective professionals should not be fitting sub-standard components to systems when the full standard is available for pennies more. The core purpose of a plumbing system is to deliver water flow, restrictions should be avoided not added for no good reason. Plumbers seem to have a tendency to claim every component of a system 'makes no significant difference' then run a mile when the overall system disappoints.

So what are you experiencing?

As I said they are flow killers on gravity systems but on normal mains pressure systems they are pretty insignificant

I would agree with marshian and JohnMo here, with one distinction. On a normal mains feed to taps, a reduced bore isolator on its own will not usually be the thing that ruins the flow, because the tap is already the restriction. It is a different matter if you have several of them in series, or on a gravity feed or a heat pump circuit, where each small restriction adds up. For telling them apart, look for full bore wording on the body or packaging rather than the handle, as handles can be swapped, and if the flow is already disappointing I would not hesitate to ask for full bore valves on the main runs while the work is still open.

@Spinny go and open one of the open-ended ones in your kitchen, and see what happens.

The water will come out of that faster than it’ll come out of the tap / other, so it exceeds that requirement.

There is no call for full bore here, unless (as said) it’s on a gravity hot feed.

The time to ask this question was obvs as the plumber was doing the job, but the question I would have asked is why some numb-nuts fitted a pair of 1/4 turn (full bore) lever valve isolators 6” from all of the ballofix isolators (the 1/4 turns tick your box so I’m lost as to the logic here)???

Remove the ballofix valves and just keep the appliance isolators (DW & boiling water tap?) if you have access to the lever valves?

On 25/10/2026 at 14:41, Spinny said:

thats got a lot going on...

On 25/10/2026 at 14:41, Spinny said:

Is there a way to tell the two apart by looking at the valve

The size of the bodies is generally visually different between full-bore, standard bore, and reduced bore for the same fitting sizes.

44 minutes ago, Nickfromwales said:

The time to ask this question was obvs as the plumber was doing the job,

Well yes and I have had different plumbers at different times. The first pic is my utility and I used temporary outside taps that were previously fitted there to measure flow rates with a couple of plumbers watching me do it. Clearly the flow would have been a little higher if they were full bore valves and no plumber ever said do you know those are reduced bore valves. I am sure the things will make no material difference to the taps, but the principle of the thing still grates. When you have flow issues I have found it strange that none of the plumbers I have had has seemed remotely interested in actually measuring flow at different points across the system to work out a solution. We just go straight into, it could be this, it could be that, it could be the other, and trial and error mode with each one often offering up a different seemingly random point of view. A frustrating approach to what should be measure, deduce, fix.

The pipework in the other pics is in the kitchen. One pipe feed leaves there to go through some conduit and around behind cabinets to exit to an outside tap. Another pipe feed goes off through conduit to a fridge freezer with ice maker and cold water dispenser. So they both need valves. There was an apprently completely unique question that arose at the time about whether hard or soft water should be fed to the fridge freezer - no answer was available from any relevant 'professional' - the manufacturer didn't know - the kitchen company didn't know - the plumber didn't know. So in the hiatus the plumber decided for himself to do the pipework so it could be switched either way.

Sadly I am increasingly exasperated by things at present. Moving forward successfuly is just so, so difficult. Some will be aware of my flooring saga - 6 months to get most of a floor done. Well after removing the foil from my bifolds (which was put up to try and keep the temperatures down so the floorer could work)... I now find there are a few faulty LVT planks that will have to be changed - a couple with manufacturing faults that were not visible until full daylight hits them - three where the laying is in error with raised lumps at the edge between one plank and another. Getting a carpenter is like a search for the holy grail.