monobloc taps for hot water in gravity systems

I changed my taps in my refitted kitchen from the traditional two tap dual input mixer to a monobloc.

The old system was fine, the new system is good for cold water, but the hot water does not come out quick enough (about 1/2 what it should be at best)

The hot water system is gravity based, the pressure is only about 1 bar, judging from the distance between the top of the tap and the bottom of the feeder tank for the hot water cylinder (1 meter). I live in a 1 floor apartment.

The tap was from IKEA, I didnt read the documentation about the minimum pressure required, and I discarded the instructions.
I've never used monobloc taps before this, I didnt think there would be a problem.

I'm guessing they require 3 or 4 bars, judging from the monobloc taps i saw in homebase.

Does anyone know if there are monobloc taps which work with low pressure ? Do I have any options apart from replacing the monobloc ?

I'm afraid that you could be in trouble with the tap as it was designed to work on higher pressures that are the norm in continental water supply systems. The pressure in your gravity hot water system is very low in comparison to your mains fed cold water supply. Your options could work out to be quite expensive. This may include either changing the monoblock to two single pillar taps or pressurising your hot water with a booster pump or mains fed sealed hot water system. Suppliers of these taps should make customers aware of these pitfalls especially when dealing with ancient irish plumbing systems.
Also be carefull that when you are using the tap in mixing mode that the higher cold mains water does not enter up into your lower pressure hot water and pressurise it. This can happen with some types of monoblock mixer taps.

Thanks Villa1
Your answer is good and it matches what I have found out from other sources.
Monobloc taps should only be used when the hot water pressure is the same as the cold water pressure.
I've got a 35mm hole in the worktop now, I've got to figure out a way of covering the hole when i take out the monobloc tap. Any ideas.

I plan to get a tap similar to the following.
[broken link removed]

I'm thinking it will work because it's similar to the old tap and it doesn't need the copper pipe to be reduced from 15mm to 8mm before it enters the tap.
I'm thinking it's similar to 2 pillar taps except there is only one outlet

Should it work ?

I had a similar problem when I had a kitchen re-fit. I bought a mixer (monobloc) tap from B&Q which turned out to be a high pressure fitting. My hot water tank is on the same level as the kitchen (I'm in a bungalow) so I didn't have sufficient pressure.

A plumber suggested I get a tap which offers more than 1/4 turn when switching it on (as a booster pump was going to cost a lot). Many of the taps have 1/4 turns but I eventually found one which improved the hot water flow - it's still not as powerful as the cold tap, but it's far better than it was.

The tap I got is the Franke Rotaflow.

LouisCribben said:

I
The hot water system is gravity based, the pressure is only about 1 bar, judging from the distance between the top of the tap and the bottom of the feeder tank for the hot water cylinder (1 meter). I live in a 1 floor apartment.

Click to expand...

You're not getting 1 bar. 1 bar is equivalent to a 10 Metre head of water, so you're actually getting 0.1 bar!

Get a booster pump.

Pique318 said:

You're not getting 1 bar. 1 bar is equivalent to a 10 Metre head of water, so you're actually getting 0.1 bar!

Get a booster pump.

Click to expand...

Exactly right Pique318

Today earlier on, I realised that I had the figures wrong by a factor of 10, but I couldnt edit the post because the way this forum software is setup doesnt let you edit an old post.......

I could get a booster pump, but surely its cheaper to change the tap, and rely on gravity ? I know gravity will work.

gipimann said:

I had a similar problem when I had a kitchen re-fit. I bought a mixer (monobloc) tap from B&Q which turned out to be a high pressure fitting. My hot water tank is on the same level as the kitchen (I'm in a bungalow) so I didn't have sufficient pressure.

A plumber suggested I get a tap which offers more than 1/4 turn when switching it on (as a booster pump was going to cost a lot). Many of the taps have 1/4 turns but I eventually found one which improved the hot water flow - it's still not as powerful as the cold tap, but it's far better than it was.

The tap I got is the Franke Rotaflow.

Click to expand...

The Franke Rotaflow may be the answer to my problem. It works at a minimum pressure of 0.1 bar, which is around what I’ve got I think.

Is your Franke Rotaflow quarter turn, the ones I came across on google search are the traditional multi turn taps ?

Is your feeder for your hot water cylinder in the attic ?
I’m in an apartment, my feeder is above the cylinder, but on the same floor

If yours is in your attic, maybe you have slightly more pressure than me coming into your hot tap.?

I think I’ll go for a Franke Rotaflow, at least I can reuse my monoblock 8mm flexi pipes and use the same 35mm hole which I drilled in the worktop.

The rotaflow is advertised as a conventional turn and definitely turns more than 1/4.

Yes, my cold water tank is about 4-6 feet above the hot water cylinder.

One thing to remember is that 8mm flexy pipes are hopelessly undersized when dealing with gravity fed hot water systems. By all means change the tap if you can but make sure to feed this tap with standard 15mm supply pipes. This is the industry standard. Smaller diameter pipoes will restrict the gravity flow from your hot water system.

villa 1 said:

One thing to remember is that 8mm flexy pipes are hopelessly undersized when dealing with gravity fed hot water systems. By all means change the tap if you can but make sure to feed this tap with standard 15mm supply pipes. This is the industry standard. Smaller diameter pipoes will restrict the gravity flow from your hot water system.

Click to expand...

Good point.
But for single hole taps, surely it always requires 8mm flexy (or 8mm non flexi) pipes ?
The hole I drilled is 35mm.
Do some single hole taps come with 2 * 15mm inputs, there would probably be just enough space at a push...

Would I be right in saying that if I want 2 * 15mm inputs, I need a 2 hole tap ?

Yes, there are monobloc mixer taps out there with 15mm hot and cold inlets. Ring around suppliers because I have seen them. You may have to get fittings that adapt to imperial/metric piping, but in some cases they come in the box with the mixer tap. Hope this helps