Combi-Boiler Shower Question

[cosmarchy]

I would like to know whether you can install en electric shower on combi boiler system?

I have understood (although I don't understand why) you cannot fit a booster pump on a combi-system but I am not sure about a non-booster pump electric shower.

Could someone clarify please?

Thanks

 

[sooey]

Yes you can use an electric shower when you have a combi. It only needs a cold feed into it and will give you some back up if the boiler goes down. Although you'll get a better shower if you use a mixer fed by the combi.

 

[baxpoti]

30Kw Combi powered shower or a 10Kw electric shower.

There's a choice.

 

[cosmarchy]

I want a shower from thje combi which is to be 30KW or 37KW Bosch... but the missus wants an electric shower...

Another thought occurs. Since neither is pumped and relying on mains pressure, is there anything I can do to help relieve low pressure should I find that this is a problm?

I am installing the bathroom upstairs, with the boiler downstairs, can you see any problems with the pressure?

Thanks

 

[gas4you]

If you suspect you may have low pressure, you need to test the cold mains pressure before purchasing the shower, indeed before deciding on which power combi as well.

Ideally for a 30Kw you will need about 14 l/min at your cold taps, which will give the 12 l/min from the boiler and about 16-18l/min for the 37 Kw. If you have 2 Bar + pressure as well, all the better.

Most 10Kw showers will need at least 1.25Bar-1.5Bar working (dynamic) pressure to let them work.

Having an electric shower is good for back up purposes, but I, along with the others above, would fit a good quality thermostatic shower off the combi.

 

[cosmarchy]

Thanks very much guys, I shall investigate further.

Out of idle curiosity, why can't you fit a booster pump on a combi system? Is it because of pressurising the mains...?

 

[dextrous]

Thanks very much guys, I shall investigate further.

Out of idle curiosity, why can't you fit a booster pump on a combi system? Is it because of pressurising the mains...?

The booster pump would have to be installed on the incoming mains prior to the combi anyway. This is, in simple terms, against the regs. As for why this is the case, I'm sort of guessing her and expect to be shot down in flames, but if you boosted water mains with a pump, then when the pump is turned off there would be a difference in pressure between the incoming supply and the pipework after the pump. This could, in theory, lead to (potentially contaminated) water being forced back into the mains. supply. Having said that, this would be resolved by installing a double check valve, so I assume there is some other reason.

 

[Fluffster]

Beacause the combi will only heat the water as it flows through and so you do not have a stored volume of water to pump from.

Pete

 

[dextrous]

Beacause the combi will only heat the water as it flows through and so you do not have a stored volume of water to pump from.

Pete

sorry fluffster - not sure I understand. There is a stored volume of water to pump from - the reservoir or pumping station

 

[Fluffster]

True however it is not a hot volume of stored water

Pete

 

[dextrous]

True however it is not a hot volume of stored water

Pete

Indeedy! Probably my misinterpretation of the ops question, which I read as basically either asking why you can't stick a pump on the mains supply before the combi, or "sucking" the water out on the hot outlet pipe.

 

[gas4you]

Combi's are designed to give a set temperature at a set flow rate. Trying to 'pull' more water through than the combi wants to give will affect its performance to say the least.

Also many combi's have a flow restrictor fitted to the cold inlet so they can only deliver this set amount of water.

You could look at fitting an accumilator if the pressure/flow you have bothers you.

 

[cosmarchy]

ok, I see. thanks for settling my curiousity.

If I wanted to do a flow/pressure test can I hire the equipment. I have had a quick look without luck but to be honest I am not entirely sure I know what I am looking for!!

Do plumbers do this sort of thing or is it something i'd have to call the water board out for?

Thanks

 

[dextrous]

Pressure tester - http://www.screwfix.com/prods/82412...onument-Tools-Mains-Water-Pressure-Test-Gauge

As for flow rate, you could use buy a weir gauge, but you'll be able to get a reasonable estimate by running water into a builder's bucket (with graduations up the inside) and seeing how long it takes to fill a given amount, then multiply up to get litres per minute.