Combi Boiler & Mixer Tap

[davidhewitt4]

Hi,

Just has a combi boiler fitted and noticed that the bath tap is acting strange.

It is a basic non-thermostatic mixer tap. I get lots of hot water with just the hot lever on, however, it goes cold if the cold lever is opened anything past a fifth of the way.

All the other mixer taps and mixer shower are fine (the one for the sink is off of the same supply).

Is it feasible that the tap is somehow the fault (its only 6-months old by the way).

Dave.

 

[lame plumber]

simple answer is to not open the cold too much then, cold mains will outdo the hot flow, simples

 

[davidhewitt4]

I know what you mean - just takes longer to fill the bath up!

Its just got be really curious about why this mixer tap is different to the rest?!

 

[lame plumber]

combis do take longer to fill than cyls, just make a cup of tea.

 

[Alpha man]

Fit a pressure reducing valve, or slow the hw tap down a little.

 

[davidhewitt4]

Thanks very much - I wondered if that would help. Definitely worth a try.

Am I correct in assuming that it will be fitted on the cold supply near the tap?

Thanks again,
Dave.

 

[supper plumb]

fit a flow reducer on the cold and a non return valve on the hot this will help
HOW NON RETURN VALVES WORK - Plumbing Tips - YouTube

 

[glenno1]

Its getting mixed in the body where as some taps get mixed at the spout

 

[lame plumber]

cheapest option for a hot bath is to run the cold turned down, simple and free

 

[stoker122]

fit a flow reducer on the cold and a non return valve on the hot this will help
HOW NON RETURN VALVES WORK - Plumbing Tips - YouTube

No need for non return valve, pressures are equal on a combi.

 

[lame plumber]

No need for non return valve, pressures are equal on a combi.

not quite true if the flow restrictor has been fitted in some makes to ensure the water heats up ok

 

[stoker122]

not quite true if the flow restrictor has been fitted in some makes to ensure the water heats up ok

Flow restrictor not pressure reducer.

 

[lame plumber]

if you have a pipe at constant pressure and flow rate, if you change one variable you will change the others as well, basics physics as described by Sir Isaac and the rest of the team. So fitting a flow restrictor can cause an apparent rise in pressure etc etc. Please dont tell me I.m wrong here, I suffered years of physics at school till I left and then used it to work with hydraulics on farm machinery later in my first working role . So I have a more than basic comprehension of how fluids work and how you can adjust one parameter to give you more power on another, comes in handy when sizing and fitting hydraulic rams and pumps.

 

[davidhewitt4]

Thank you for all of your comments - much appreciated.

The explanation regarding mixing in the body seems exactly right because both mixer taps that work ok are sink type (which I assume mix at the spout). The dodgy one has the inlet pipes apart and a chrome cylinder between them (then the spout).

I'll have a look for a reasonably priced pressure reducer for the cold - they seem to be between £20 and £30 from what I can see if that sounds about right?

Thanks again,
Dave.

 

[davidhewitt4]

Thanks very much for all the help and advice - much appreciated.

The point about mixing in the body sounds exactly right. The two mixer taps that are OK are upright sink style - the dodgy one has inlets spaced apart and a chrome cylinder between them (and the spout in the centre).

Just so I'm clear, is it a pressure reducer or flow restrictor that would be best on the cold? (I've tried turning down an isolation valve on the cold but assume this won't affect it in the right way)?

Thanks again,
Dave.