Hi folks,
The subject line says it all - fitting a new kitchen and finally got round to putting the sink and tap in this w/end and I have an issue with the hot water.

Tap is a normal Franke ceramic disc mixer with 10mm copper tails. I've gone from the 15mm in the house to the tap via service valves and 15mm flexi p/fits with 10 - 15mm adapters.

Turn the hot on full and I get not-a-lot. More than a dribble but not much. It's not spitting and farting at me. (the missus is - but that's a subject for another forum!)

Crack the cold and the flow increases but goes completely cold after 2 or 3 secs.  Cold is always ok.

Turn the cold off again (with the hot still running) and its cold for 5 - 10 secs then goes hot again.

If I open the washing machine hot valve with the hot tap still on, and drain it to the sink I get the same low pressure flow, except when I close the w/m valve then I get a burst of high(er) pressure from the hot tap, then back to the same low pressure.

Whilst waiting for plastering and fitting carcasses etc etc the hot feed to the kitchen has been unused for about 3 weeks.  Could this have a bearing on it?

Any clues?  All you can suggest would be gratefully received as it's taking me forever to do the washing up. Sorry about the long post. Great site fellas, full of useful info - you guys should write a book!

Cheers,  

As JerryD says strictly speaking you should have a check valve on the Hot pipe to stop the Cold water (mains) mixing in the tap and going back down the hot supply pipe.

Also as said you may well have an airlock on the Hot pipe, you can use the physics as above to clear the airlock. Simply put your thumb over the tap spout and open the hot tap and then slowly open the cold so that the mains pressure clears your airlock.

Right again JerryD, the only possible way round this is to install a 28mm non return valve, sounds ridiculous I know but it wouldn't restrict the flow any where near as much as a 15mm one.

Fellas thanks for your prompt replies.

The now-down-the-tip 25 year old compression valve mixer worked just fine so I'm hoping for an airlock - thanks for the tips for getting rid of them - I'll have a go and see what happens.  15mm copper tails on the old tap, btw.  

Incidentally, I've read back through some of the old topics to find an answer before my original posting and one of the tips for getting rid of airlocks suggested a length of hose between the mains cold and hot tap to dispell the airlock but the results were predicted as 'could be messy'.  What is the likely outcome of trying this method?

A pump may have to be considered however, as we are in a bungalow and hence have a lower head of water.  I reckon theres a couple of meters max between the tank base and a tap anywhere in the house.  The taps in the bathroom (both non-mixer compression valve) were and are working fine.  The hot water tank is in the bathroom, on the same level as the kitchen tap.

Did I just buy the wrong type of tap, or are some more suscepible than others to this problem?

The tap has a third valve supplied via a filter so we've no chance of drinking the mixed hot and cold so no worries there.

If I fit a 15mm check valve in the hot feed and the tails are only 10mm, will it restrict the flow as much as a 15mm check valve on a tap with 15mm tails?  (Does that make sense???!)

Cheers everyone.  

[quote author=rustynuts  link=1129059405/0#6 date=1129154741]

Incidentally, I've read back through some of the old topics to find an answer before my original posting and one of the tips for getting rid of airlocks suggested a length of hose between the mains cold and hot tap to dispell the airlock but the results were predicted as 'could be messy'.  What is the likely outcome of trying this method? [/quote]

All you will be doing is sending mains pressure cold water back up the hot tap to the tank.  This will push out any air, just let it run for long enough to do this.  The hot pipe will then be full of water rather than full of air and water.

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Not good then, 0.2 bar  


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These won't have 10mm tails I'm sure


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This makes no difference, it's the height of the cold water tank that gives the pressure to the hot taps

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Possibly yes, with such a low hot water pressure, 10mm tails + check valve is expecting rather a lot

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That's good  

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The same, it's still a 15mm check valve

My advice is to make sure you haven't got any airlocks.  If you are sure there is no air in the pipes then you either have to pump the hot or change the taps for low pressure type.

The Tri Flow is a lovely system, one thing you must check is that the installer checked the water pressure before putting it in. The filter has a maximum pressure listed in the fitting instructions.

[quote author=JerryD  link=1129059405/0#11 date=1129241280]

If you look on the Franke website on their TriFlo taps they say:


NB. Ceramic disc taps in certain installations or where there is a low head of water (below 4 metres) may not provide adequate flow rates.

Whoops......   [/quote]

Bugger!   Still, could be worse.

Didn't have any luck with clearing any air in the pipes so I guess we're stuck with it unless I stump up the $$$$ for a pump.

Cheers,