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Can you get decent shower pressure with a combi boiler?

(18 Posts)
IShouldBeSoLurky Tue 12-Jan-16 17:56:10

Just that, really. My head has been turned by all the posts on here about Megaflos and I would love one, but not sure budget and space will permit, and it does seem like overkill for a 2-bed, 1-bathroom house. However, after 4 years of shit shower pressure, water pressure dropping and shower running cold if a tap is turned on in the kitchen/the washing machine is running, I really, really want a decent shower when we move. We're redoing the bathroom anyway and I suspect we will have to put in a new boiler.

BackforGood Tue 12-Jan-16 17:59:57

Sorry, no help to you but I'd like to know the answer too so marking place wink

Spanglecrab Tue 12-Jan-16 18:17:25

It depends. You can't get more out in the hot side than you have coming in on the water main. Some of the larger combos can deliver near 20 litres per minute. They wouldn't reach that with 10 litres per minute coming in. Fill a large container and try to time how many litres per minute the cold tap in the kitchen delivers.

IShouldBeSoLurky Tue 12-Jan-16 18:21:45

Thanks Spangle. So in theory the shower can deliver the mains cold water pressure up to the limit the boiler is capable of?

PigletJohn Tue 12-Jan-16 18:22:52

1) yes

2) but only if you have good flow being delivered to it.

UK plumbing design was, for about two thousand years, lead pipes with small diameter delivering water to a cistern where it was stored until required. It did not matter that the rate of flow into the house was slow. If you want to use water at the rate it is delivered, you need a bigger water pipe all the way to the main in the road. Unless you are lucky enough to have a house that already has a large pipe, you need to dig a trench through your front garden and lay one. 25mm will do but 32mm is better. You may also need to run a larger pipe to the boiler, and from the boiler to your bathroom. you will also need a larger stopcock and any service valves must be full bore (they are more expensive than the 70p leaky ones found at merchants and in skips, so some builders are reluctant to fit them).

Fill a bucket at the cold tap in your kitchen sink (and at the garden tap and utility room, if you have one), time it to full, calculate how many litres per minute you get. It will also be useful to know the colour and diameter of the pipe supplying your stopcock.

Pressure is not the same as flow.

PigletJohn Tue 12-Jan-16 18:24:00

too slow

IShouldBeSoLurky Tue 12-Jan-16 18:32:53

Thank you so much. So just looking at boilers now, 14L/minute seems to be the rate the mid-range ones can deliver - is that right? So we'd need our mains flow to be the same or greater?

It's a Victorian house in London if that makes any difference. I'll check the flow rate tomorrow when we get the keys grin

IShouldBeSoLurky Tue 12-Jan-16 18:37:07

Also, running a new pipe from the main in the road sounds like a massive job - is it?

PigletJohn Tue 12-Jan-16 18:56:41

Easy for a sturdy woman. If you can dig a trench for your runner beans, you can dig a trench through your front garden.

Some plumbers are weedy so might employ a labourer.

Your water co may have a list of approved contractors. They will want to inspect work done by others and charge for connection. If the pipe is lead, they may have a lead replacement scheme. Ask them to test the drinking water for lead content.

If you want 14lpm hot water delivered to your shower, you need more than that delivered to your house, because you will be mixing it with cold, and other people will be running taps and flushing WCs while you are in the shower, thus sharing the flow.

A Victorian house in London is quite likely to have a 3/8" internal dia. lead pipe, which may have got bent or squashed over the last 110 years, and have a pathetic flow. It might also leak. You might get a leaky pipe replacement subsidy. If you have a new water meter fitted they might connect it free.

A Victorian house probably has wooden boarded floors that are easy to lift to run the new pipe underneath. It need not follow the same route as the old one.

IShouldBeSoLurky Tue 12-Jan-16 19:26:48

You are SO helpful, thank you flowers

I am not the digging type but will look into all your suggestions.

Chapsie Tue 12-Jan-16 19:30:31

If you are planning to change the bathroom and therefore shower-
I settled on a Mira platinum digital for Gravity fed system which had a pump built into it - great shower smile

RiverTam Tue 12-Jan-16 19:34:00

We're in a Victorian house and ours is fine. I have absolutely no idea about the size of the pipes, we've been here for 11 years and have never done anything to them, but the water pressure in the shower is fine. Takes donkey's years to fill the bath though...

pippistrelle Tue 12-Jan-16 19:45:14

I know nothing of pipe sizes and trenches, but I do know that we had a combi boiler fitted last week and the shower is INVIGORATING compared to the rather feeble trickle we had when the water was coming from a tank. I didn't even realise how feeble our previous water flow was, so, for us, it's a great unsought perk of having a new boiler.

PigletJohn Tue 12-Jan-16 19:51:57

"pressure in the shower is fine. Takes donkey's years to fill the bath though..."

"Pressure is not the same as flow."

Aaaaar.

IShouldBeSoLurky Tue 12-Jan-16 20:01:57

So how is it possible to have a decent pressure shower if the flow rate is low? Sorry, am clueless about these things.

PigletJohn Tue 12-Jan-16 20:34:47

Imagine a hypodermic syringe full of water. Press your thumb on the plunger with all your strength. The water squirts out of the needle at great pressure. But the flow is 10ml in ten seconds. It would take you days to fill a bath.

Now hold a bucket of water level with the top of your head. Tip it over. The water has almost no pressure. But the flow is ten litres in half a second.

You can get reasonable pressure from a shower at low flow by having a small spray head. If you put a big drencher head on it, the water would dribble out, even though the amount of water might be the same.

You can't get more flow, or more pressure, than the incoming pipe (or tank) provides, unless you add a pump.

insideout Tue 12-Jan-16 21:01:00

We run a mira adept of a 28kw combi, it runs very hot and is almost too powerful! We live in an edwardian house with horrendous plumbing ( and a stonking great lead pipe laid under 4ft of concrete) but once we had the boiler installed the shower was great ( previous owner ran it off its own gas water heater)

IShouldBeSoLurky Tue 12-Jan-16 23:16:36

Yes, I do see the logic of the syringe vs bucket argument! I think my view is clouded by the fact that in my last property I had a shower with syringe-like holes for the water to come through (was off a hot water tank, GOD how I regret not asking the bathroom fitter to put a pump in!) and the pressure was pathetic and got more so as the tiny holes clogged with limescale over time.

Insideout, that's so encouraging to hear smile

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