Combi Boilers

[SteamyTea]

Why do people fit these for showering.

 

I am staying up at my Mother's house in Third World Buckinghamshire.

Carers turn up, so I nip into the shower, carers fill a bowl of water to wash my Mother's arse, or whatever they do.

Flow reduces, water goes cold, then temp becomes scalding, after a couple of minutes all back to normal.

This is a 30 kW boiler, and the tap down stairs does not have a great deal of flow.

Now I know that accumulators and flow valves can be fitted, but really, combis are rubbish, reminds me of the one I had in my first house back in '84.

So things have not moved on in 36 years.

[ProDave]

Yep I have thought that for a long time.  I just hate the whole concept that the water temperature coming out of the tap varies with the flow rate of that tap, and that is before you even consider turning other taps on in the house.  And then the fact you turn a hot tap off, then turn it on a minute later and you get warm water to start with (what was in the pipe), then some cold water before it warms up again. 

 

People like them for "simplicity" but what's complicated about a system boiler and unvented hot water cylinder (as long as you avoid 3 port mid position valves) They just give a nice constant temperature regardless of flow rate and regardless of what other taps are on.

[JohnMo]

They are designed to provide a fixed temperature for any given flow, winter water temperature are lower than summer, and manufacturers install a flow restrictor on the water inlet to give year round ok performance, an increase delta T is required in winter; due low cold water temp being lower.  Flow when inlet water is at its coldest is rubbish compared to summer, the restrictor gives worsening summer flow also. With a flow restrictor installed flow will be down 10 to 15% on advertised rates.

 

However as with most things they tend to follow the path of least resistance, so open a tap and flow is diverted there instead of the shower.

 

So could be a couple of reasons for the rubbish performance

 

Plumbing arrangements giving biased flow to the outlets closest to the boiler.

 

Shower mixer not responding to change of flow of hot water.  It should be an adjustable TCV, so manage the temperature set even with flow changes.  So flow rate reduces, not go cold/hot.

 

The easy fix on new build, manifold to individual users.

 

For new or old systems Canetis Superflow on inlet and removal of flow restrictor.  This give s 30 deg inlet temp to boiler, giving improved flow.

 

Shower mixer that control temperature not just rate of flow for hot and cold.

[SteamyTea]

28 minutes ago, JohnMo said:

Shower mixer not responding to change of flow of hot water.  It should be an adjustable TCV, so manage the temperature set even with flow changes.  So flow rate reduces, not go cold/hot

It has one of those, but is rubbish  or don't work.

I am with @ProDave fit a cylinder of some sort.

[ProDave]

3 minutes ago, SteamyTea said:

t has one of those, but is rubbish  or don't work.

It could well be the thermal mixer cartridge has failed.  If you live alone so nobody else uses a tap while you are in the shower you might not notice it has failed and is just working as a manual mixer valve.

[SteamyTea]

1 minute ago, ProDave said:

It could well be the thermal mixer cartridge has failed.  If you live alone so nobody else uses a tap while you are in the shower you might not notice it has failed and is just working as a manual mixer valve.

Could be.

Not going to worry about it house will be up for sale soon I think.

[JohnMo]

3 hours ago, SteamyTea said:

reminds me of the one I had in my first house back in '84.

So things have not moved on in 36 years.

Don't think most plumber (there are exceptions) do anything different from what was done in 70s.  They still plumb the same way, no reason to change, as no one asks for anything different.  Very few use hot and cold manifolds for example, which distribute hot water more evenly

[SteamyTea]

9 minutes ago, JohnMo said:

Don't think most plumber (there are exceptions) do anything different from what was done in 70s

Wish they would go back to the 70's, system boilers and a tank of hot water. Dead easy to understand.

But even that gets complicated as they fit UVCs.

[JohnMo]

But the tank would have pressurised from a tank in the loft, and had really bad flow all of 3m head (less piping losses) in an upstairs bathroom.