Hot Water Flow Rate

[Ian123]

I had a Combi boiler installed about 6 months ago, and have just had my new bathroom fitted.
I now have the problem that when the shower is running if i operate any other hot water tap the shower cuts out (due to the thermostatic valve).
The flow rate of my boiler should easily cope:
DHW Flow Rate (Delta T @ 35) 13.5 litres/min
Also the hot water pipe leaving my boiler is 15mm would this this restrict my flow? and should it be 22mm
My bathroom fitter believes this to be down to the Cold water supply pressure to the house, but i am not convinced as i can have have several cold water taps on at once.

Any other ideas?

 

[Doctor Drivel]

I had a Combi boiler installed about 6 months ago, and have just had my new bathroom fitted.
I now have the problem that when the shower is running if i operate any other hot water tap the shower cuts out (due to the thermostatic valve).
The flow rate of my boiler should easily cope:
DHW Flow Rate (Delta T @ 35) 13.5 litres/min
Also the hot water pipe leaving my boiler is 15mm would this this restrict my flow? and should it be 22mm
My bathroom fitter believes this to be down to the Cold water supply pressure to the house, but i am not convinced as i can have have several cold water taps on at once.

Any other ideas?

Measure the flow rate in litres per minute filling a bucket and time. What is the pressure like? Irrespective, The combi should have its own dedicated cold feed back to the main stoptap. Take cold for the shower off this cold feed just before the combi. Check stoptap. Change to a full type.

Fit flow regulators on all outlets to balance up supplies if further trouble.

 

[Ian123]

thanks,
I've done the flow test and found it to be lacking at around 9l/min so i will be getting in touch with the company that installed my boiler.

Thanks for your suggestions

What does a flow regulator look like, i can only seem to find restictors on the web.

 

[Corgigrouch]

But is your Delta T really 35C ?

If you look in the catalogues then this is the temp rise that is always stated as a benchmark yet 35C is a bit useless. You may well find that the actual flow rate is a fair bit less and is restricted in the boiler in order to achieve a higher Delta T

Water will always take the easiest path so if it is easier for it to flow through the tap, then this is where it will go rather than the higher resistance of your shower

 

[Ian123]

[But is your Delta T really 35C ?

If you look in the catalogues then this is the temp rise that is always stated as a benchmark yet 35C is a bit useless. You may well find that the actual flow rate is a fair bit less and is restricted in the boiler in order to achieve a higher Delta T

Water will always take the easiest path so if it is easier for it to flow through the tap, then this is where it will go rather than the higher resistance of your shower]

Would you then suggest that 9l/min is a reasonable flow rate for the spaec stated and the solution would then be flow regulators?
Is a flow regulator just a valve?
[/quote]

 

[simond]

Most boilers are set to a higher Delta T, 42C is not uncommon.

Therefore a 13litre quoted flow rate at 35C Delta will be proportionally less at 7C higher. Circa 20% less in fact.

Combi Boilers are usually rated at 35C to give users a comparative measure of their hot water efficiency.