Typical Combi Hot Water Pressure

[Rom]

Hi

Im in the process of buying a house, which has a Bosch 28i Junior, fitted on the first floor, in the room next to the bathroom.

The bathroom is an old avocado green suite! So has to go, Im trying to find a suitable shower.

I can find plenty of flow rates, and minimum working input pressure, and minimum input to get maximum flow. But nothing to suggest what kind of pressure I can expect out of it.

We have been looking at the Thermostatic Panel types, which mostly recommend 2 bar minimum. Are these going to be out of the question?

Failing that, a thermostatic valve type, which seem to range from 0.1 bar, to 1 bar recommended.

A little unsure if a combi counts as low pressure or high pressure.

Thanks

 

[Dan Robinson]

It is mains pressure.

Mains pressure varies.

You need to test the property's supply.

 

[Rom]

So the combo itself doesn't alter pressure?

I'm thinking just because my mains cold pressure is say 5 bar. Doesn't mean the hot from my combi will be 5 bar?
So testing my cold mains on a washing machine pipe, will give me my hot pressure?

 

[bernardgreen]

Some combi boilers require that a pressure reducing valve is fitted in the mains supply to the boiler. Typically these are set at 3 bar.

Cold water at 5 bar would not be a hazard other than getting wet, hot water jetting out of a tap and into a wash basin at 5 bar could be a hazard of scalding

 

[wannocks]

The boiler will slightly reduce the pressure and flow rate. The only way to know for sure is to measure it.

 

[muggles]

So the combo itself doesn't alter pressure?

I'm thinking just because my mains cold pressure is say 5 bar. Doesn't mean the hot from my combi will be 5 bar?
So testing my cold mains on a washing machine pipe, will give me my hot pressure?

You're confusing pressure and flow rate. Your static pressure is the same no matter what you choose to put on your pipework. Your available flow rate is what you actually want to know,and that will be restricted by the performance of the boiler

 

[Rom]

The boiler can do 10l/min at 35c rise I think.

The shower specs aren't asking for flow rate. Which is what's probably getting me mixed up. They are saying a minimum pressure.

So I can obviously measure the flow rate from the hot tap. But this doesn't give me the pressure does it.
But if the gist here, is that a combi won't greatly reduce pressure. Then I can do a pressure test on the cold washing machine pipe. Which should be roughly what I get out of the boiler hot side? Obviously if the cold is say 10bar, the boiler will reduce this via a flow restriction to about 3 bar as said above?

Or is there a tool I can buy to actually measure the hot pressure.

 

[muggles]

OK, gizza clue, no idea which shower you've chosen!

 

[bernardgreen]

Obviously if the cold is say 10bar, the boiler will reduce this via a flow restriction to about 3 bar as said above?

A flow restrictor is not intended to reduce the pressure, only restrict the flow ( but invariably this does also reduce the pressure )

A pressure reducer in not intended to reduce the flow, only the pressure, but reducing the pressure will invariably reduce flow through the resistance of pipework down stream from the pressure reducer

 

[bernardgreen]

A flow restrictor is not intended to reduce the pressure, only restrict the flow ( but invariably this does also reduce the pressure )

I missed a bit.

( but invariably this does also reduce the pressure when the flow rate through the restrictor is close to the maximum permitted flow rate )

 

[Rom]

Just as an example, something like this perhaps. Though would probably be concealed.

https://www.victorianplumbing.co.uk...xHnJmLTB8_HPD3owNdx1SuCO-eZYItjM53hoC0O3w_wcB

Which says 1.5 bar minimum. Now if a combi will struggle to get much over that, then I won't bother with this style. But at 3 bar, it's doing 9l/m. Which is in range of the boilers flow rate.

But that is irrelevant if the pressure isn't enough?

 

[muggles]

You need to consider both flow and pressure. Put a pressure gauge on a tap and measure flow rate through a different tap. Set it to 9 l/min and see what pressure you have.

You also need to consider that unbranded/own-brand kit like that will be almost impossible to get spares for when it breaks, and buying concealed units which are unbranded is a terrible idea for that reason - you end up smashing tiles off the wall to dig them out and replace them

 

[Rom]

Cheers. I hadn't even thought about spares / breaking.
Just thought that style looked nicer than a normal mixer type.

All quite complicated really. Glad I've asked, rather than buy a shower that will work poorly.
I'll have a look for a gauge that can go on a tap. Only seen the washing machine type.

 

[jeff the gasman]

If you can't stop the cold water flow at the kitchen tap with your thumb your shower will be fine.