monobloc causing no hot water despite non return valves

[pmcx9]

i have fitted a new kitchen sink and monobloc tap. The tap kit had 2 non return valves so i fitted on both hot and cold feeds. The hot pressure is now very low to non existent.
i have stripped it and checked and no blockages. the cold is mains and the hot is from an immersion tank and it is situated in a ground floor flat.

am i right in guessing a monobloc is not suited to a flat because the cold pressure is far, far greater than the hot and subsequently overpowers the non return valve on the hot side?
or should i only have fitted one non return valve?

just sitting here with no water at present so any help appreciated!

 

[breezer]

i am not a plumber but it sounds like there is not enough pressure to overcome your non return valve on the hot, i presume the cold side works?

 

[pmcx9]

yep, pressure on cold is very good. i am just fitting a ballofix valve to cold side to try and reduce pressure to see if that help. i hadnt bothered until now as the cold feed is directly above the stopcock. i am putting the ballofix just below the non return valve so it wont affect cold supply to the bathroom

i assume if i remove the non return valve on the hot side it will result in the cold sending water back to the immersion tank when mixed setting is selected

 

[Nige F]

You assume right You really need a Bi-flow mixer. there are some about, but they cost more

 

[pmcx9]

i presume a bi flow mixer would require at least a modicum of pressure on the hot side?

i have deduced the pressure on hot side is so low it can barely push open the non return valve. i havent even got the cold feed connected so this must be the case

can a monobloc be run without a non return on the hot side if i ensure the cold feed is low by only slightly opening the cold ballofix valve or is this a no-no?

 

[chrishutt]

Why did you fit non-return valves?

 

[pmcx9]

i am no plumber (in fact i am jack of no trades) so.....

i fitted non return valves because the tap came with two flexi pipes down to 10mm and two 10mm to 15mm non return valves. i didnt have any 10mm compression fittings so assumed the non return valves are necessary and could attach to the subsequent 15mm ends

 

[ChrisR]

If the tap mixes the H & C within it then the non return valve on the hot is not optional. But you would be a lot better off of you took it out and replaced it with a normal one in the pipe. They have a much bigger area so are much easier for the water to open. Make sure you get a single check valve and not a double check valve (which is just 2 in series).

£1.07: http://www.bes.ltd.uk/products/graphics/8149.gif

 

[chrishutt]

Fair enough. It sounds as if this sink mixer may not keep not and cold separate, as most do. Does the hot water (such as it is) emerge from the inner part of the spout outlet and the cold the outer part?

 

[pmcx9]

it is a sorrento chrome lever action monobloc from howdens (MFI trade arm) Tap3601
it does appear to mix within the tap because when i turned on the cold without the hot feed connected and selected mix then cold water came down the hot feed inlet.

the non return valves are separate.

from your advice guys it appears i need a monobloc tap that does not mix within the tap and therefore i could leave off the non return valve on the hot side.

 

[chrishutt]

Correct! Or boost your hot pressure with a pump?