Could I daisychain an electric shower and a thermostatic mixer shower?

Posted by specofdust@reddit | AskUK | View on Reddit | 19 comments

Hi all, I currently have a manual mixer shower which is okay but a bit lame, fairly low flow rate, and the boiler loves to give you a shock of cold / boiling every few minutes leading to constant adjustment. So I'm thinking thermostatic mixer, which sorts out the variability issue, but not the pressure issue. My boiler evidently isn't capable of providing sufficient hot water to provide me with good flow rates. I don't have a tank, it's a combi, so power shower is out. Could I get an electric shower installed purely to heat up the cold water side of things, and then feed that into the "cold" side of a thermostatic mixer, so that instead of having 10C "cold" side I could have 25C cold side, and therefore much higher flow rates from the cold side, and therefore higher overall flow rate? I can't see any reason it isn't technically feasible. I know in theory I could just buy a much better boiler but that's very expensive and overall the boiler I've got is good, and well suited to the flat I'm in, it's just showers in the UK are mostly awful and I want something that could strip paint and drown a duck. Cheers for any info!

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19 Comments

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blaireau69@reddit

What's the make, model and age of your combi? Probably best getting a decent electric shower fitted, Mira Sport 10.5kW.

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specofdust@reddit (OP)

WB, Greenstar 25 SI MK IV, so in the region of 7-13 years old. Potentially it's too old, pretty sure the expansion vessel is knackered so might just replace the whole thing. Honestly don't understand how you can enjoy a shower under anything with the Mira label on it, but nice for you that you do so!

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blaireau69@reddit

> Honestly don't understand how you can enjoy a shower under anything with the Mira label on it I don't know what you mean by that. I've fitted 27 or 28 Mira Sports, everyone has been delighted with them.

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specofdust@reddit (OP)

I mean, I get the feeling I'm puncturing your professional pride a bit here. If a tradey fitted a shower for me I would be gratefuland say thanks that's great etc. etc. - you don't make the showers you just fit them (presumably, at least). But they're absolute garbage compared with a power shower, I can piss with a higher flow rate than most Miras can manage when the water is just-about-lukewarm. God forbid you want a hot shower, if you're lucky you can angle the shower head basically horizontal and the water might actually dribble onto your head then. I've used a great many Mira showers over the years, they're fitted in pretty much every cheap rental flat in the country, they are reliable, cheap, simple, I'll give them all of that. They do the job, miserably, but they do it, I can give them that.

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Tumeni1959@reddit

It might work, but why not just install the electric shower on its own? Pitfalls; if you turn off the thermostatic shower, but forget to turn off the electric, that will probably lead to the electric overheating, or triggering any overheat safety device. You'd effectively be blocking the output of the electric, as if its output pipe was blocked. Also; isn't a "manual mixer" just another name for a thermostatic mixer?

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specofdust@reddit (OP)

Electric showers are limited to a maximum of 10.8 kw, which just isn't enough power for a decent shower. I had considered the issue with burning out the motor in the electric, I would need a constant supply of cold to the shower basically as you'd have in a regular electric shower, then just turn the electric on to provide "cold" water to the thermostatic mixer, and hot on the provide the hot, and that should function fine. Also, no. Manual mixer is where you have manual control of each valve (tap), thermostatic mixer has the valves automatically controlled by a thermostat.

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blaireau69@reddit

> 10.8 kw, which just isn't enough power for a decent shower Utter nonsense. Mira Sport 10.5kW is an excellent electric shower. I've installed at least 2 dozen of them, have one at home. All clients very happy with them, as am I and my family.

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specofdust@reddit (OP)

Honestly? UK standards for a "good" shower are ridiculously low. I don't know if it's just a cultural thing, or just that the average Brit has never stepped under a high pressure high flow rate shower before, but once you actually understand what showers can be like, UK showers almost all lie somewhere between the range of "utterly dismal" to "depressing".

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Pale-Imagination-456@reddit

I have sometimes wondered about adding in a small "under sink" micro tank or instantaneous heater myself.

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kunstlich@reddit

Have you checked your shower head for a flow restrictor?

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specofdust@reddit (OP)

So, there's nothing obvious, it's just a standard el cheapo shower head connected to the half inch hose. I suspect no-one would have bothered fitting one as I live in Scotland so we don't have metered water and you can use as much as you want.

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kunstlich@reddit

It's a little, usually plastic, insert on the inside of the shower head. If you take the head off the hose you might see one. If you bought your shower head in the last 10 years it most likely has one fitted, but they're fairly easy to remove. It's not going to blow your hair off by taking it out, mind.

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specofdust@reddit (OP)

Appreciate it, that's given me maybe a 5-10% increase in flow. My hair is still there, but I'll take improvements, even if I want more.

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Chilton_Squid@reddit

A combi boiler should easily be able to provide enough warm water for a shower, it sounds like there's something wrong there and you're trying to massively overengineer a solution which won't be as good as just fixing the boiler.

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specofdust@reddit (OP)

I'm getting 5.58 litres per minute of just hot, doing a quick check there. With the cold tap cracked to its normal, I get about 8 litres per minute. I would like that to be about doubled. My boiler seems to be okay, it works fast, it turns on quickly, it's been serviced most of its life cos my flat was a student flat so had to have annual gas safety checks.

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johnsslutwife@reddit

I just wrote out a whole long reply, but realised you just need to get your boiler fixed. It should be able to hold a stable flow temperature, and if it’s giving out 5.58 l/m of just hot, that’s great as long as you’ve set the hot water flow temp high enough at the boiler. My shower (thermostatic mixer) is fed by a 50C tank on the hot side and I mix in cold to get an overall flow of 4.4 l/m, which seems great for everyone who’s used it

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specofdust@reddit (OP)

So, I think in this case we maybe just have different standards. You say 4.4 lpm is great, I get about 8 lpm from my shower and I think it's mediocre at best. 4.4 lpm and I'd probably be installing a high powered electric just to get away from that. Maybe water pressure has an impact? Hard to say for sure. It's a good shout that getting a boiler tech out to have a check of thing is probably worth it, but it's set to a fairly high temp for the water and after mixing like I say I get 8 lpm, which just isn't sufficient for me. I would prefer a minimum of 12 lpm and preferably in the 15 lpm region.

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SanchXX@reddit

You can get a water pump installed or get a all in one unit with pump boost build in. [https://www.plumbworld.co.uk/power-showers-191-0000](https://www.plumbworld.co.uk/power-showers-191-0000) I think those are what you looking for.

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specofdust@reddit (OP)

It is very much not, unfortunately. As I said I have a combi boiler, no tank, so traditional power showers are out.