No hot water. Any cure?

[cardiffrob]

We have a curious problem in our new house. You can run hot and cold water through some of the mixer taps but the cold seems to overpower the hot feed and then back-flush the hot water line with cold water. Is there a solution to this? The shower works alright with a pump to it but all other taps, to one degree or another, will do this back-flushing thing. If you run a bath with both taps open it merely fills the bath with ice cold water!
I've tried to work out the design of the copper 'spaghetti' at the back of the tank but am stumped. How can you balance the pressures without having a pump running full time to keep the hot pressure up?

Any suggestions would be gratefully received. The walls are about to go back up on the extension so now is the best time to sort this out and I don't know any other sensible websites inhabited by grown-ups.

 

[ford34/2]

same sort of problem, we have what I`m told is poor pressure off the water main, turn on the upstairs taps, fine, turn on the downstairs and the upstairs goes to a trickle. no one come up with a cure, water board dont want to know, before the combi boiler was installed, you could back fill the hot water cylinder by turning on the kitchen mixer tap, the cold pressure went up the hot feed and into the cylinder till it overflowed out to the cold tank and then it overflowed when the level increased above the overflow. Elec shower sometimes cuts out when you turn another tap on as the pressure drops, house is only 47 Yr old.

Stan

 

[cardiffrob]

Sounds exactly what I've got. The shower works well, too well in fact. Can strip meat off of the bone.

Ideally I'd like to increase the water pressure on the hot side but I'd guess it would be the more expensive option?

 

[lazybones51]

Ford34/2 : When they fitted the combi boiler I imagine they took the cold water tank out (normally in the loft), which I imagine would have feed your upstairs taps. The kitchen tap would have been off the water main, so having them both on wouldn't have been a problem as they are drawing from different sources. Does that make sense? Now everything is off the water main, you get the drop in pressure when multiple taps are open.

 

[ajlelectronics]

I am no plumber or expert in these matters, so I may be talking rubbish of course.

Could you use a header tank in the roofspace to get some pressure back? The low pressure mains feed could fill that at its leisure. For continuous hot water from a combi, my experience is that although the hot is low pressure, if you reduce the cold flow to match the hot flow temperature you want, it will work OK. I can't see how a tap can allow back siphoning.

 

[rtbcomp]

It could be the design of the mixer tap. The best ones mix the water at the nozzle, the swan-neck has 2 separate ducts inside it. Others mix the water at the bottom of the swan neck, which can allow one circuit to feed back into the other, although it's usually the cold that feeds back into the hot as Ford mentions in post #2.

As you mention a tank I'm guessing it's not a combi boiler?

To get a proper balance between hot & cold on a conventional tank system you need to take the cold feed to the taps from the bottom of the cold water tank if you have cheapo mixers.

A check valve in the hot line would stop cold water feeding back, but you wouldn't get any hot water either if the cold tap was turned on.

The simplest solution would be to fit individual taps instead of mixers or a decent mixer.

 

[TechnicAl]

We have a Pressure Reducing Valve on the cold water input. Got it from screwfix. Don't know if that's what you need but we had similar problems and its worked for me

http://www.screwfix.com/p/honeywell-22mm-pressure-reducing-valve/68966

 

[bigegg]

I have same problem with my bath mixer.

I resolve it by turning the hot water tap on full until it's running hot, then turn cold water on in small increments to get the temperature I like from the tap

 

[mike os]

in situations where the cold is mains and the hot is gravity (off a tank) the tam needs to have separate flow paths (ie the hot & cold mix at the exit) and/or be fitted with check valves in the low pressure pipework, to prevent backflow.

in te meantime half closing your mains stopcock to reduce flow will help

 

[normspanners]

Not that it helps I know,
But I have the opposite -------------- I am always in HOT water!!
generally from the missus.


Check the diffuser on the outlet of your tap The sister inlaw had this sort of problem I removed the airator's and it cured some of the problems, it doesnt mix the water as well but stops the back feed.
as rtbcomp says I did exactly that, I fitted a separate 22mm feed from cold feed tank, for bath/ shower pump / bidet mixers etc and when I fill the bath I put both on full, and can fill the bath in 3 minutes, but have my hot water super hot 75/80deg in the tank, so that we can shower 4 people, one after the other, ie give you more hot water, but for the hand basin and kitchen taps they should be fed direct from the main .

 

[pedrobedro]

If you are using stored hot water and there is a long run to the hot tap leave the tap till the water runs hot before you turn the cold tap on. I've never heard of cold water back feeding into the hot before but we have separate taps, can't be doing with this new fangled stuff.

 

[the snooper]

If you are using stored hot water and there is a long run to the hot tap leave the tap till the water runs hot before you turn the cold tap on. I've never heard of cold water back feeding into the hot before but we have separate taps, can't be doing with this new fangled stuff.

if both hot and cold are fed direct from mains it wont be able to back feed as the pressure would equalise

 

[pedrobedro]

if both hot and cold are fed direct from mains it wont be able to back feed as the pressure would equalise

Round at the shop the hot water and heating is supplied by an on demand system. If the pressure is equal wouldn't the hot be supplied at the same pressure as the cold ? It comes out a lot slower, I don't understand the mechanics of the system but presume the boiler throttles the cold water and only releases it at a pressure where it is able to maintain the set temperature. I like to understand these things, I've removed and refitted radiators on the system and refilled the heating circuit by means of the loop to the recommended pressure but the hot water side just does it's own thing does it ? Our hot at home is gravity heated and fed from the tank with a good header tank above but it runs cold till the pipe run is emptied of cold and all our cold is at mains pressure. If hot water was available via the mains it would save us a fortune.

 

[upinsmoke]

Hi Bathroom mixer taps are fine as long as they are fed at the same pressure. So you could go for mains pressure unvented hot water storage, or suppy your cold inlets apart from the kitchen sink tap, from the the tank in the loft

 

[the snooper]

Round at the shop the hot water and heating is supplied by an on demand system. If the pressure is equal wouldn't the hot be supplied at the same pressure as the cold ? It comes out a lot slower, I don't understand the mechanics of the system but presume the boiler throttles the cold water and only releases it at a pressure where it is able to maintain the set temperature. I like to understand these things, I've removed and refitted radiators on the system and refilled the heating circuit by means of the loop to the recommended pressure but the hot water side just does it's own thing does it ? Our hot at home is gravity heated and fed from the tank with a good header tank above but it runs cold till the pipe run is emptied of cold and all our cold is at mains pressure. If hot water was available via the mains it would save us a fortune.

Yes the cold water into the boiler will be throttled but if back fed the pressure would equalise

 

[ford34/2]

of course years ago with hot water cylinders and Showers there was an overwhelming tendancy to plumb straight off the hot system, being gravity fed for the the hot water in the house , then some plonker would connect the cold side to the mains. Instead of a feed off the cold storage tank to equalise out the two supplies of water to the shower. Then people wondered how the shower was crap.
On our system now the cold is fed off the direct water riser into the house, prior to the Combi this was also the way the system was on the cold side. the hot off the Back boiler warmed up the Cylinder which was pressured off the tank in the loft.
Just with the current Combi a Bosch Worcester trying to feed multiple hot taps in the house is always and has always been a problem, maybe the combi cant chuck out enough flow to saisfy the needs of a couple of taps and has the mains pressure regulated back.
I cant get my head round how the system allows a back fill from cold system to hot system through the taps unless you have all mixer style taps? and the mix is inside the mixer outlet, as previously said many mixers only mix at the very end outlet- helping to avoid a back fill situation. Out of curiosity, whats the boiler situation, what heats the Hot side. back boiler and tanks or a combi style on demand.

Stan

 

[cardiffrob]

Pulled the ends off of 2 of the mixer taps (Kitchen and utility room) and one has the mix at the outlet end whilst the other, which is a problematic unit, has the mix at the tap itself and then a long hose to the nozzle. I had a look at a pressurised water tank but it is going to cost something into four figures to fit one. Currently I have a conventional gas boiler and copper tank, all new from British gas 3 years ago.

If it was a car exhaust system then it would be a good idea to make the exhaust bore larger and fit a straight-through silencer to lower the back pressure, wouldn't it? Does that analogy work?

 

[ford34/2]

Looks like change the Mixer tap and problem probably solved. Or never turn both taps on at once on that mixer, then cold cannot overpower the hot pressure and back feed into the hot causing it to overflow into cold header and then possibly to the outside overflow.
Or maybe consider putting in a flow regulator on the cold somewhere under the Sink with the problem Mixer tap. something like this £3.99 screwfix,-- for 2

Stan

 

[marfyboy]

quick fix stick a single check valve on the hot. if a combi is fitted it should be equal pressure' cold water mains into the combi same pressure out in the hot within reason. if its a system boiler as mentioned above your feed tank to the hot water would overflow mainly at night when there is no demand on the hot water. shower pump? if its mains pressure DHW you would rarely need one unless your cold water pressure was low then the cold wouldn't be pushing up the DHW. comes down to cost either replace the mixer that's passing or stick a pressure reducing valve on the CWM incoming or on the basin at fault.
just my thoughts

 

[Barlidge]

Looks like change the Mixer tap and problem probably solved. Or never turn both taps on at once on that mixer, then cold cannot overpower the hot pressure and back feed into the hot causing it to overflow into cold header and then possibly to the outside overflow.
Or maybe consider putting in a flow regulator on the cold somewhere under the Sink with the problem Mixer tap. something like this £3.99 screwfix,-- for 2

Stan

My kitchen sink has a mixer fed by mains cold and hot from tank, Just underneath the sink I have an isolating valve like this fitted to the cold feed and have it closed enough so the when both taps are full on its a nice warm temperature. Works a treat and is probably the cheapest/easiest fix.