Shower Install - Combi Boiler

My plumber friend informed me that the hot / cold water pressure didn't look enough to run a mixer style shower direct from the hot / cold supply.
We talked about options and arrived at.

1. Electric Shower (Would Rather Avoid this).
2. Lagged hot water tank in loft with electric immersion heater on a timer, then can have power shower or just more pressure (gravity fed prefered option).
3. New boiler (definately not this option)

Does anyone have any information on the cost/efficiency of immersion heaters? Is there any way I can heat (all or in part) the water for my shower from my existing system more efficiently? Perhaps using an electric immersion and the hot water from the boiler to top it up?

Any advice / experience greatly appreciated.

Lots of combis are used to heat a cylinder and would be the cheapest way of heating it compared to the immersion.

the only problem is getting a balanced pressure of hot and cold for your shower. Has the pressure/flow been measured? Maybe worth addressing the route of the problem!

From what you've said i believe your considering buying a cylinder so you can have more pressure from the increased head of water and a pump if needs be to power a mixer shower. If this is the case then i would suggest an unvented cylinder which can be directly heated from your boilers flow and further more the unvented cylinder's are fed from your cold rising main and hence run at mains pressure (no need for a pump). If it is just to power a shower then micro unvented cylinders are available and are no more than a metre high. A company called OSO makes these cylinders at a very reasonable rate and they come in about five times cheaper than say a megaflow unvented.

PS are you sure there isn't enough pressure combi boilers usually belt out more than enough for a mixer shower. My pressure feels low at the taps (combi boiler) but being a plumber i know my taps reduce the flow somewhat. I also have a mixer shower that is extremely powerful from the combi.

The mini Oso cylinder is only 5l capacity, probably too small to run a shower from! The smallest off the shelf direct Oso is then 100l. Wserle seems to be looking for the cheapest option for running a shower so any additional cylinder/storage is out until it has been confirmed that the flow rate is insufficient for a shower. Pressure is not the main issue.
As long as the combi is supplied with its max rated flow there should be no problem with a shower.

First job then is to confirm your available flow rate (from a tap before the boiler)

Great thanks for the advice if I can simply fit a mixer it will save so much anguish (and cash!), a few more questions:

1. Can I simply measure the flow rate using a measuring jug and stopwatch, and should it be the hot water flow rate(although I guess this is the same as the cold in a combi boiler system??)?
2. What is a good flow rate?
3.How do I measure the pressure of the water is it the indicated pressure on the boiler?
3. Whats a good pressure for a shower?
4.Do you simply devide the flow rates / pressures by two to indicate the likely shower output?

Thanks again.

Yes stopwatch and a bucket.

Depends on what combi you have.

24Kw = 9-10 l/min

30Kw = 11-12.5 l/min

35Kw = 14-15 l/min

It's very unlikely that either your mains water flow or pressure are too low to run a shower. For most showers you only need around 10 litres/min flow, say up to 8 litres/min of that through the combi.

Open a cold tap fully and see what flow rate you get, then open a hot tap and measure that, then open both together and see what you get. Report your figures back here.

You can measure the flow rate by timing how many seconds it takes to fill a bucket of known capacity. for example if the bucket holds 5 litres and takes 15 seconds to fill then you have 20 litres/min flow rate.

Boiler is directly below bathroom in kitchen.

Cold Water Upatirs in Bath ~ 17 liters/minute
Cold Water upstairs sink ~ 20 "
Hot Water upstairs in Bath ~ 10 liters/minute
Hot water upstairs in sink ~ 10 "

I'd like to note that the rate can be variable day to day and these are probably toward the fastest we get.

So should a mixer be fine?