after changing kitchen mixer tap hot water just a trickle

[zvonko kracun]

hi, i have a gravity system in my house. non-pressurized boiler and i have no space to lift my cold water cystern or hot water tank, i also don't want to buy or run an electric water pump. due to a leak in the housing, i had to change my old dual lever monoblock mixer tap, which run beautifully with good warm water flow ( non ceramic). bought one advertised to work from 0.5 bar, which is a modern looking single lever mixer tap with pull out spray. now i only get a trickle of hot water, cold water fine of course. i did change the connecting tails just in case, but they are the same. i also did take out all the reducers from the new tap. the hot feeds from a 22mm pipe, the isolation valve is a 22mm full bore one. there is no air or dirt in the system and the other warm tap in the house works fine. it is the bathroom tap, a single lever monoblock mixer.... without me knowing i must have been sold a large-bore version, although it has these tails, with 5mm connectors and not much bigger pipes to fit into hot and cold ( unfortunately unbranded, the shop i bought it from, has closed years ago, and being a bathroom tap it wouldn't fit in the kitchen anyway) do i have to install an old-style 2 lever tap with 15mm connectors? has anybody run into the same problem and found a solution? is there a a "single lever mixer tap" that would work ?

[Nick Odell]

We had a similar problem out here in Argentina when we were sold one of those fancy pull-out taps in place of a bog-standard version. The water heater here is not a combi boiler and demands a flow of 5.5lpm in order to trigger the combustion. The ordinary tap would do this so comfortably that I never saw any need to measure the flow while it was installed: the pull-out version delivered barely more than 4lpm and was useless.

We have sidestepped the problem by turning on the kitchen tap, walking into the utility room and turning on the sink hot tap. The combined flow kicks the boiler into life and then turning off the utility room tap allows things to carry on as normal despite the slower water flow. Ridiculous is it not - and probably not too safe either as I suspect others on here are about to tell me. But hey - this is Argentina!

I think the fluid friction - or whatever it is called - in the water line is just too much unless you have a massively higher water pressure than we do. If the utility room dodge had not worked, the next step was going to have to be to swap the shower hose (because on our tap, the flexible connector is nothing more than a repurposed shower hose) for a shorter length or modify the existing one to be as short as possible while abandoning any pull-out feature. From trial and error with the tap partially disassembled I think most of the friction seems to be in that final hose so maybe a short hose and pulling out any water filters and aerators in the shower head will give you back the oomph you need. In my opinion you have nothing to lose by trying and it might prevent you having to buy a whole new assembly.

Good luck and do tell what happens!

Nick

[zvonko kracun]

thanks nick, you gave me an idea. the supplied hoses are ridiculously long indeed. i had to loop them for installation. i shall trace and install as short as possible ones , if it works, i post the result. thanks for your help. zk

[John Rumm]

How much hot water pressure do you actually have (i.e. how far about the tap is the cold water cistern)?

[charles]

0.5 bar is 16ft of water head. how high above the kitchen is your tank?

[Tim+]

?To work?, not actually to be any good.

Nearly all modern taps are designed with mains pressure HW as that is what is common in most of the civilised world. Alas, in the UK we have (for historical reasons) a lot of gravity systems.

See, it?s working! ;-)

I think you?ll be lucky to find a mixer tap with pull out spray head that is any better. If you?re determined to have that kind of tap and you?re not planning on moving house anytime soon consider a move to either a pressurised system, a pumped system or a combi.

Shortening the tails won?t hurt, but I think you?ll still be disappointed.

Tim

[zvonko kracun]

yes, tank is 2 meters in hight and 4 meters horizontal away from tap. cistern is half a meter above tank. my main problem I think now is the length of the tails but especially the pull out spray which is almost another meter long. I intend to try a tap without pull out spray and I use very short tails. thanks for the suggestions. zk

[Chris J Dixon]

Depending upon the construction of the tap, the problem may be check valves incorporated in each line to prevent them back-feeding.

These were not needed with the older design of mixer, where the flows were separate all the way to the nozzle.

Chris

[Andy Burns]

I did get a kitchen mixer (the tall inverted 'U' style) with concentric pipes all the way to the nozzle about 8 years ago, a quick search seems to say they're not as easy to find now ...

[Chris Green]

Yes, I hadn't realised there has been a general change. I wondered why a new mixer tap I recently installed stays cold longer than the older one I have at the kitchen sink even though both have under-sink water heaters.

[zvonko kracun]

thanks chris, can you send a picture of said tap, or a link ? i have almost given up using my new tap. apart from the half meter tails, by design , the spray pull out, is attached to the smallest of flexi pipes ( 5mm where connected ), it is over one meter long, looped outside and of course both hot and cold are looped inside, to feed the spray, in an extremely small space . considering the possible presence of back feed prevention check-valves i fear i have to buy an old style mixer tap . the only thing which keeps me back is that my other tap in the bathroom is a modern mixer tap with long tails. it branches off from the same warm water feed, installed at similar hight. it does not have a pull out spray..... and this might be the major problem with my new kitchen tap ?? anyway thanks again for your help. zk

[Andy Burns]

Here's one which can handle hot pressure down to 0.2 bar (2 metre head)

searching for gravity fed kitchen taps, or low pressure kitchen taps does find a few, but I doubt you'll get a "fancy" one with flexi-hose.

[zvonko kracun]

great andy, this is excellent. a million thanks. light at the end of the tunnel !! now comes the big job, persuading my wife, to give up on the good looking modern tap. zk

[charles]

Your problem is almost certainly insufficient head for that tap. The length of the tails will not affect the water pressure.

[zvonko kracun]

thanks Charles i am aware, for that kind of tap i need to move house. seems simpler to buy an old-style tap or find a similar one i have in the bathroom, which is a single lever mixer tap. zk

[John Rumm]

Its the vertical height that matters - the more the better. The horizontal matters far less, although the less the better.

So it sounds like you have at most 2.5m of head or about 0.25 bar which us below the minimum for that tap.

So the only options you have are find a new tap that will work at a lower pressure, or, add a pump.

(pipework changes will make little difference)

[zvonko kracun]

i have found one with stated 0.1 bar functionality ( old style, monoblock, two levers, washers, 15mm straight copper feed tails ) and one

0.2 bar single lever mixer, ceramic ( better looking ) . difficult to decide.

[Tim+]

But they will affect flow to a degree. The long hose to the pull-out head will also add considerably to flow resistance.

Tim

[John Rumm]

Not quite that drastic - you could fit a DHW booster pump to raise the HW pressure. You could change the cylinder to an unvented one that runs from the cold main, and so does not need a cistern tank at all, and runs at high pressure directly.

[zvonko kracun]

have just bought a 0.1 bar tap. amazingly.... these are still available. thanks everybody. zk ps without pull out spray !