Adding hot water storage to a combi system to allow pumped shower

Why spend money on an inferior system?

get a pressurized tank and drive that from the combi.

Because as far as I can tell the pressurised tank relies on the flow of the incoming mains. The combi boiler is not running flat out, so if I could get a higher mains throughput I wouldn't need any other solution.

I am exploring solutions where I can add a meaty pump to get a much higher flow rate than you would get from pressurised mains flow.

As far as I know you are not allowed to "suck" on your mains input. Otherwise I would be looking at adding a pump on the mains before it enters the boiler.

Cheers

Dave R

That entirely depends on your mains pressure.

Even with the current reduction my showers are 'more than adequate'

You can get cylinders which contain a diaphragm behind which is a fixed mass of compressed air at a certain pressure. They fill up from the mains. When you run a shower the air pressure acts on the diaphragm to push the water out faster than the mains pressure allows, and the cylinder empties. They then refill from the mains via a valve until the pressure is equalised again.

If you get one that's enough to hold the water for a shower, that'll give you a pressure boost. As soon as you turn off the shower it'll start refilling, ready for the next shower.

They only need to be as big as you need for a single shower, but you might want to put one on the input side of an unvented cylinder (ie cold water, since they typically aren't insulated). Some of the units fit in kitchen cupboards, so eg if you have an annoying corner cupboard then that could be a place.

Theo

Booster pump?

Interesting. Of course, if I can increase the mains flow I don't need the pressurised cylinder. The flow rate through the combi is the issue, not the ability to heat the water.

In a previous house I had a smaller combi and a much faster flow of water. Which is why I am pretty sure it isn't the boiler.

Cheers

Dave R

You could do that...

I think the first port of call would be to work out why the current flow rate is so poor. If you measure the incoming rate (stopwatch and large container of known size) at your best performing tap, you will have a starting point.

Next work out what the theoretical limit of hot water delivery is from your combi. (for example a 24kW combi should do something in the order of 9 to just under 14 lpm of water at 40 deg C (depending on the incoming water temperature)

Under 12 lpm, and you can use mains booster pumps to take it upto 12. If you need more than that, then an accumulator tank fed from the mains might be an option - that can supply water faster than it is replenished for a while.

Both the latter options would boost flow rate all round the house on both hot and cold.

Either would also allow fitting an unvented cylinder to heat from the combi. Slightly less faff than needing a header tank, and would also do away with the need for shower pumps.