Best power shower method from Combi boiler

i will get this done first then, then we will see where we are up to!

Good Lad

potterballs said:

the shower pod im putting in is item number 220609498626 on a famous auction site (im not sure if your aloud to mention names)

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I wouldnt buy that if i were you. No way you'll get a decent steam/shower unit like that for that sort of money. I had to install something very similar also bought from ebay back early last year for someone, build quailty was shocking, instructions were half in chinese and gobbledegook and apparently the custard has had no end of problems with it.

Have a look at your washing machine, normally they are connected to the water supply with a valve, see

//www.diynot.com/shop/WASHING_MACHINE_VALVE_15_X_3_4_BLUE__RED_HANDLES/6842

If so pop into your local plumbers merchant and get a test gauge, see

//www.diynot.com/shop/Monument_Tools_Mains_Water_Pressure_Test_Gauge/15747

Switch off the blue valve and disconnect flex hose to washing machine, be prepared for a little leakage as the flex line will have residual mains pressure in it. Connect up the test gauge to the valve and open the valve. Hey presto you now know your supply pressure.
Test gauge is about £12.

close the valve, remove the gauge (again a little leakage) and reconnect the washing machine hose open valve and check for leaks.

Whitworth said:

If so pop into your local plumbers merchant and get a test gauge, see

//www.diynot.com/shop/Monument_Tools_Mains_Water_Pressure_Test_Gauge/15747

Switch off the blue valve and disconnect flex hose to washing machine, be prepared for a little leakage as the flex line will have residual mains pressure in it. Connect up the test gauge to the valve and open the valve. Hey presto you now know your supply pressure.

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Which is only half the equation. You can turn your stopcock down till the cold water tap only drips - but you'll still be able to get good static pressure. You need to know what sort of pressure is available while drawing off the required flow rate - if it hold up enough then you're OK, of not then some rethinking is needed.

There is a fourth option not mentioned yet - thermal store (or heat bank). Mains pressure hot water, if selected correctly can be much higher output than combi (run two shows or show+another tap), decouples heating from boiler so you can run an all-TRV heating system with modulating pump AND get the boiler to condense most of the time instead of hardly ever - and you can have an immersion heater for emergency backup if (or rather when) the boiler breaks down.
I put one in my flat - so far it's working very nicely. I can run both the bathroom sink and bath hot taps on full and still get nicely hot water out.

As I see it, these are the options :

Combi boiler. No need for hot water tank or header tank so doesn't need much space. Most plumbers seem to think they are God's gift to mankind and you'll have no trouble getting them serviced. Against: they are more complex than heat-only boilers and reliability seems to be lower by reputation, hot water flow rate is limited by boiler heat capacity, and you end up with a boiler that's usually grossly oversized for the heating.

Open vented hot water cylinder. Gives good hot water flow rates, but at low pressure (basically the pressure is limited by how high your header tank is). Needs space for both HW cylinder and header tank. If tank is run cold, you will have to wait for it to reheat.

Pressurised (unvented) hot water cylinder. Main pressure hot water, but moderately expensive and can only be fitted (by law) by a suitably qualified/registered plumber. Multiple safety valves (=expensive) and should be checked/serviced every year for safety. Particularly if used with an immersion heater or any uncontrolled heat source, there is a risk of superheating and serious injury/death - people have died in the past from these rupturing and the contents flash boiling, hence the safety valves etc and legal restrictions which should prevent future reccurrances.

Thermal store/heat bank. Stores heat so not reliant on capacity of boiler - but internal coil thermal stores still have a hot water output limit (usually more than a combi that would be specced for the job). Heat banks can have huge power outputs - one common model boasts of a 100kW rating for the heat exchanger. Being open vented they are no more hazardous than an open vented hot water cylinder.
As long as you have enough head, then they can be heated direct by the boiler, rather than using an indirect coil - faster and more efficient, and you can run the boiler at full output in condensing mode most of the time (in short bursts). Since they should normally be reheated top-down, recovery is rapid and even if you ran the store cold, you;d be able to get hot water fairly quickly after starting up the boiler. The boiler will start once the store temperature starts dropping - so effective duration is significantly enhanced since you have the stored heat plus the boiler capacity available.
And you can run the heating from the store as well, so the boiler isn't running in a fairly inefficient regime to keep the house warm. Modulating pump and fully TRV system is both quiet and comfortable.
Moderate downside: they need space like any other hot water cylinder, but no header tank.
Big downsides: few plumbers have heard of them and most are likely to have a huge sucking through teeth before telling you you need to rip it out and bung a combi in; and cost - they are significantly more than any of the other options.

Which is only half the equation. You can turn your stopcock down till the cold water tap only drips - but you'll still be able to get good static pressure. You need to know what sort of pressure is available while drawing off the required flow rate

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Good point I stand corrected.
Would it be acceptable as a rough measure of flow rate to open the bath tap fully and put a bucket under it for 15 or 30 seconds, then measure the amount of water in the bucket? Whilst doing this someone could monitor the pressure gauge and see how much it drops when the tap is opened?
Could then the experiment then be repeated with two taps running (the bath and the kitchen sink) to see the effect on the flowrate in the bathroom?

Whitworth said:

Which is only half the equation. You can turn your stopcock down till the cold water tap only drips - but you'll still be able to get good static pressure. You need to know what sort of pressure is available while drawing off the required flow rate

Click to expand...

Good point I stand corrected.
Would it be acceptable as a rough measure of flow rate to open the bath tap fully and put a bucket under it for 15 or 30 seconds, then measure the amount of water in the bucket? Whilst doing this someone could monitor the pressure gauge and see how much it drops when the tap is opened?
Could then the experiment then be repeated with two taps running (the bath and the kitchen sink) to see the effect on the flowrate in the bathroom?

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I guess something like that - though for the shower you aren't interested in the max rate your can draw, but how much pressure you can maintain with the shower at it's normal flow rate and another tap turned on.


Just to add to my earlier summary ...

Of the four main options, only the open vented cylinder doesn't supply mains pressure hot water. However, it is also the only one that has a usable store so you can still use the hot taps if the cold water goes off - whether that is an issue depends on what your supply is like, we have a good supply here.

Of the four, the combi and heat bank options also require your electricity to be on. The combi to run the boiler, the heat store to run the pump. The rest will continue to give you hot water - stored hot water for the hot water cylinder (open-vented or unvented), stored heat for the thermal store.


Whether mains pressure hot water matters is to a point a matter of preference. It certainly makes mixers etc easier to control if the hot and cold are at the same pressure, and it also removed the problem of a leaky mixer allowing backflow from the high pressure cold to the low pressure hot.

I'm just about to refit my bathroom.

I have a standard Potterton Profile 80e boiler (23kw) feeding an indirect hw system with vented cylinder. (as wellas heating the house via a closed presuurised ch system). Both are pumped. Currently two thermostatic showers are fed from this cylinder using a twin pump.

As well as the two showers I am now adding a bath/filler diverter concealed bath that requires minimum 1bar, therefore I am replcing the twin shower pump with a whole house pump to run the two showers and the bath.

Yes I am going to run out of hot water very quickly!!

I am thinking of upgrading the cylinder to a telford Typhoon (160ltr), which apparently recovers heat very quickly (30%) faster due to fins on the heat coil.

Any suggesting or experiences of this type of setup?

Thanks.