No hot water. Any cure?

[julianf]

we have 3.5bar pressure hot water to the bath (pressure reducing valve on the coil in the thermal store) and mains pressure cold.

if both taps are on full, the flow is mostly cold, as the flow takes the path of least resistance (ie the direct cold path)


ive never considered this to be a problem at all. i just dont turn the cold full on.


the actual combined flow is (to all intents and purposes) the same either way, so its not like the bath fills any slower - just more water comes from the hot tap to compensate.

again, our set up does exactly the same, but its really never caused us enough bother to even think about it until i read this thread! : )

 

[DAPPH]

T'is a common thing , the incoming mains is say 10 psi when free flowing through a tap and the pressure coming out the boiler has been dropped due to various restrictions in the boiler so the outlet flow pressure is much blower say 7psi.

Solution :-
A single element pressure pump with an adjustable outlet pressure 2 metres of pipe work out from the boiler hot water outlet . This means you can match the cold water free flow .
Wickes used to do a good range of brass bodied pumps both single & dual element that ran rather quiet if set on a high density hard foam rubber pad .
you'll find them in the area of shower booster pumps

At one place we lived we had such low incoming pressure i could nearly pee as fast as the incoming water. I put a large header tank in the roof void on a reinforced platform and pumped the head'ed water to the boiler & cold taps under pressure the only thing that was not on the rising main was the cold supply to the kitchen sink, the bathroom sink & the dishwasher cold fill for it's not a sound proposition to have home tank stored water fed to these due to the great likelihood of harmful bacterial growth .
There was a bit of a problem .. you could only use the power shower for 12 min before the pump outstripped the tanks supply . My lass soon learnt to take a little kitchen timer with her to the shower room after she came out a dead shower covered in suds & shampoo , having to wait for 12 min or so for it to refill enough for the thing to work long enough to complete her shower.

 

[Wedg1e]

We have a similar problem at Nursy's place, it only affects the main bathroom sink mixer tap. I think the issue is that the tap is an internal-mix design, so if you err towards the cold side it rams cold water back up the hot feed.
Everything else in the house works fine: the shower is pumped from DHW storage tank and cold header in the loft, each with their own take-offs so if anyone turns on another tap the shower remains unaffected.
The nearest I came to a fix was to fit service valves to the mixer tap inlets and have the cold one open just a crack, but the sink takes an age to fill - I end up shaving under the trickle of hot water and finish before the sink's half-full.
I was under the impression that internal-mix taps were contrary to the water byelaws for the same reason that you're not supposed to leave a combi attached to its fill loop - in case stored water gets back into the mains...

 

[DAPPH]

Don't you have to fit a non return valve on the mains pressure cold line to the mixer or is there one integrated in the mixer tap at the inlet point these days Byelaw 94 etc & all that ?

 

[hunter27]

It sounds like you have high cold main pressure and poor hot water pressure caused by (cold storage tank not being very high) you could fit a pump to the hot outlet from the cylinder after the shower take-off but as you probably know they are quite noisy, or you could fit a water governor in a suitable position to balance the cold pressure down to the offending outlets.
The problem now is that most modern taps are designed for pressurised systems often only having 10mm tails rather than the old 1/2 -15mm connections (not including bath taps) so really restrict the hot water flow.

Your cylinder should be piped something like this.
http://www.upperplumbers.co.uk/images/Text/Hot_water/Plumber_Hammersmith_Indirect.jpg

A bit about low pressure taps
http://www.sinks-taps.com/category-77-Low_Pressure_Taps.aspx

Hope this helps