Only lukewarm water at max setting; Thermostatic Shower

[showerguy]

I have recently fitted a thermostatic external mixer shower in my bathroom. The problem is that when it is set to the highest possible temperature its only luke warm at best. The hot water in my house is generated from a combi boiler which should be able to deliver a hot water flowrate of 12.5L/min. The boiler doesnt seem to be the problem as both bathroom and kitchen hot water taps in the house produce hot water without issue, and the boiler was only serviced last week.

I have checked that the cold/hot water pipes are the right way around into the shower bar and i have tried to calibrate the hot water delivery from the bar buy removing the temperature control knob and adjusting it but it already seems to be at its highest setting.

Does anyone have any other ideas? Id say im a DIY enthusiast but this has me stumped! Shower and boiler details in my house are posted below.

Ripley Round Thermostatic Dual Head Shower Set in my bathroom (Brushed Brass Niagara Equate Round Thermostatic Dual Head Shower Set 9301BRS - https://www.rubberduckbathrooms.co.uk/niagara-equate-round-thermostatic-dual-head-shower-set-brushed-brass-9301brs)

IDEAL HEATING LOGIC MAX COMBI C30 GAS COMBI BOILER (https://www.NoLinkingToThis/p/ideal-heating-logic-max-combi-c30-gas-combi-boiler)

 

[Chuck]

Try measuring the flow directly by timing how long it takes to fill a 1 litre jug with 'luke warm' water.

According to Plumbing World, your shower is specified to deliver 22.6 litre / min at 3 bar, which is a typical supply pressure.

 

[John.g]

12.5lpm probably refers to a temperature rise of 35C which is I believe is the normal standard means this is a 30kw combi??

The (my) mains temp right now is 14C so running that shower flat out at 22.6LPM means a showering temp of max 33C, lukewarm, the flowrate must be reduced to 17.9LPM to get a showering temp of 38C which I assume is being done??

 

[Ben-gee]

It is possible that the cold is crossing back into the hot supply, the shower valve should have non return check valves to prevent this. Make sure these are functioning correctly.

Does the shower get hot if you only turn it on to approximately 1/2 it’s flow rate?
If so it is caused by too much flow through the boiler when at full bore, as described by Johng above.

To overcome this - fit flow restrictors before each head, 15lpm should do it. But get a selection pack so you can find the best one to suit your needs.

 

[marvin]

12.5lpm probably refers to a temperature rise of 35C which is I believe is the normal standard means this is a 30kw combi??

The (my) mains temp right now is 14C so running that shower flat out at 22.6LPM means a showering temp of max 33C, lukewarm, the flowrate must be reduced to 17.9LPM to get a showering temp of 38C which I assume is being done??

Thanks

It is possible that the cold is crossing back into the hot supply, the shower valve should have non return check valves to prevent this. Make sure these are functioning correctly.

Does the shower get hot if you only turn it on to approximately 1/2 it’s flow rate?
If so it is caused by too much flow through the boiler when at full bore, as described by Johng above.

To overcome this - fit flow restrictors before each head, 15lpm should do it. But get a selection pack so you can find the best one to suit your needs.

Thanks for everyone's responses.

The hot and cold each have non return check valves which seem to be working (they open and close easily when i push them).
The shower gets a little hotter when turned on to 1/2 its flow rate initially but then cycles between luke warm and cold continuously.

I have no flow restriction on the hot water plumbing reaching the shower, although i do have an accessible hot water isolation valve. When i half close the valve the water from the shower is definitely a little hotter but no where near the temperature i would expect for its maximum temperature setting.

Should i go ahead and fit flow restrictors in each showerhead (15slpm)? or should i put a flow restriction on the hot water plumbing feeding the shower?

 

[John.g]

Can you measure that flowrate with the shower at 1/2?, also ensure combi DHW setting at max (if settable) and monitor its temperature (even by hand). If staying constant then surely has to be a shower mixer problem if shower temperature unstable?