Could 4 bar static pressure prevent shower off combi getting hot enough?

[WaterTight]

Or rather it gets hot enough but only when turned to almost full hot or higher. With the taps if you turn them on a little it's very hot, turn them on full and it's almost cold.

Would a PRV be first thing to try? Or could it be something wrong with boiler?

Shower is new so not cartridge adding to issue.

Thanks

 

[rocketmanbkk]

Is it adjustable? I mean is there like a safety trigger inside that's not in the correct position?

 

[Simon F]

whats the flow and temperature rise?
whats the boiler doing when the shower is on?
is there a control to limit the flow through the shower?

 

[jtsplumbing]

Check shower installation instructions & see what Max water pressure for that shower is, some are quite low

 

[WaterTight]

whats the flow and temperature rise?
whats the boiler doing when the shower is on?
is there a control to limit the flow through the shower?

not sure
sounds like it's firing and working normally but not gas safe so not clued up enough on that side of things
nope. but it's rated for 1 bar min to 5 bar max when in use, 10 when not so presuming 4 static shouldn't be an issue? it's a mira combiforce.

 

[WaterTight]

would a flow restrictor fitted to shower hose have the same effect as fitting a PRV? even though the taps struggle (too hot when on slightly, too cold when on full) i don't think they're that fussed about them.

 

[mfgs]

You need to check the temperature rise at a certain flow rate and then make sure it matches the manufacturers instructions. Do any other taps have this problem or is it just the shower?

 

[WaterTight]

All hot outlets suffer from slight difficulty in maintaining temp and are very hot when slightly open, nearly cold when fully open.

 

[ShaunCorbs]

what size combi in installed?

 

[WaterTight]

Not sure, did look at it but don't really know what I'm looking for. It's a very small bungalow though.

 

[ShaunCorbs]

Not sure, did look at it but don't really know what I'm looking for. It's a very small bungalow though.

as normally if combi only has a flow rate of 10 (heating) and say your flow rate incoming is 20 etc it cant heat the water fast enough,

this is why it may heat the water when the tap is half closed but not when its fully open

 

[rocketmanbkk]

If all outlets are affected I'm going with its not a shower issue. Mira are very good imo.

 

[WaterTight]

as normally if combi only has a flow rate of 10 (heating) and say your flow rate incoming is 20 etc it cant heat the water fast enough,

this is why it may heat the water when the tap is half closed but not when its fully open

Yeah I was thinking something like that. They've got a boiler bloke coming to do something shortly anyway so I told them to ask him if it could be anything to do with boiler. If he says no I guess a PRV might be worth a shot?

 

[ShaunCorbs]

Yeah I was thinking something like that. They've got a boiler bloke coming to do something shortly anyway so I told them to ask him if it could be anything to do with boiler. If he says no I guess a PRV might be worth a shot?

only prob prv reduces pressure and not flow rate which i think is your problem

 

[WaterTight]

Hmm. Well since they aren't fussed about taps I guess a flow restrictor in shower would be the answer.

 

[WaterTight]

...Unless the boiler is playing up/undersized/powered

 

[ShaunCorbs]

...Unless the boiler is playing up/undersized/powered

paying up fair enough but undersized/powered is on about flow rates

 

[WaterTight]

i think i need to go back to school with regards to the relationship between pressure and flow, always found it confusing.

 

[WaterTight]

i just tell myself pressure is how much it wants to get out of the pipe, flow is how fast it does when it gets it's chance. but i would have thought fitting a prv would automoatically reduce flow too....?

 

[ShaunCorbs]

have a read

Reducing Flow vs. Reducing Pressure - Which is it? | CTG CTG Technical Blog

 

[WaterTight]

Very interesting, thanks. Not sure it covered why fitting a PRV wouldn't reduce flow too though? It's got to hasn't it? If all other things are kept constant?

 

[ShaunCorbs]

Very interesting, thanks. Not sure it covered why fitting a PRV wouldn't reduce flow too though? It's got to hasn't it? If all other things are kept constant?

prv only reduces pressure and flow rate by the internal resistance of the valve (nothing much)

have a look at these as they might help

http://www.robertpearson.co.uk/robertpearson/images/downloads/flow-regulators.pdf

 

[WaterTight]

I like the iso+flow restrictor.

That'd presumably be a good retro fit for when people have turned down an individual iso (like on a tap to a small cloakroom basin) but it then becomes noisy

 

[ShaunCorbs]

I like the iso+flow restrictor.

That'd presumably be a good retro fit for when people have turned down an individual iso (like on a tap to a small cloakroom basin) but it then becomes noisy

just need to find the flow rate of the boiler now so you can match them up, then all you need to do is install them onto the shower pipes

 

[jtsplumbing]

Think it's going to come down to what boiler is producing, if it's a old style combi poss. 24Kw flow rate is going to be low around 8/9 lts pr min + the factor the incoming cold water temp is quite low this time of year, so boiler struggles to reach + maintain water temp.

 

[chris watkins]

Water Flow Control Products by Aquaflow Regulators Ltd

It is most likely that you need to reduce the flow on the cold side as much as controlling the flow through the boiler to end up with a stable showering temperature. It is all about the flow rates not the static pressure, so try using these rather than a PRV.

The shower is mixing cold & hot, if the cold is providing more, you are having to open the hot side up so much that the boiler is not capable of delivering hot water at a high enough temperature for the thermostatic control to work and deliver a suitable shower temperature.

Lots of shower manufacturers use to supply the brown or green restrictors to be put into the cold inlet side to sort this out when you were initialling them.




Sorry slow typist so most of my post already covered. If they are not so worried about other fittings just try a yellow or brown on the cold side as it should bring the shower back in range.

 

[WaterTight]

Lots of shower manufacturers use to supply the brown or green restrictors to be put into the cold inlet side to sort this out when you were initialling them.

Yeah actually I think/hope that's still not uncommon, I've fitted a few within the last couple of years that did.