If the bathroom is a long way away from hot-water source, I recall a post where @PeterW suggested connecting the hot pipe also to the WC cistern so that flushing the toilet would pull through the dead-leg of cold water in the pipe. (I searched but could not find the old post.)

 

Is this still considered a good idea?  My bathroom will be about 15m from the hot-water source (a Sunamp).

I don’t think it’s a good idea.

 

I’ve heard it about in the past, but to me it’s not an industry standard solution so would rather go with the return pipework which is designed to solve this problem.

 

what happens after the dead leg is away and you are then flushing the toilet with water you have paid to heat?

 

Would love to hear an estate agent list this as a selling point?

 

It may reduce condensation.

4 minutes ago, SteamyTea said:

It may reduce condensation.

 

True, although I was told that Geberit cisterns, which I am choosing, are insulated anyhow.

When I remember seeing this discussed, you would not feed the WC with raw hot water, rather you would feed it from a thermal mixing valve with that set to the lowest temperature it can go.  so the first flush will draw hot water through the pipe but when the hot arrives, the mixing valve would then reduce that to a lot less hot water so the next flush is not wasting much hot.

 

I would be looking for a thermal mixing valve that can be adjusted down to say 20 degrees?  Is such a thing made?

 

Is there a legionairs or other risk filling an open vented cistern with luke warm water and leaving it to stand?

1 minute ago, ProDave said:

you would feed it from a thermal mixing valve with that set to the lowest temperature it can go.

 

That makes sense. Looking online, the lowest temp for a TMV I found was 30º. Google in my hands could not find one that went lower.

We have the return loop with motion / light switch activated pump (which also triggers MVHR boost extraction) and it works great. You may not always be using the loo in a bathroom and may just want to pop in to wash your hands.

I'm considering using a urinal PIR sensor/valve to dump the contents of the line to drain when you walk in.

3 minutes ago, Bitpipe said:

We have the return loop

 

Yes, nice solution. But I am aiming to avoid the extra complication of a hot return.

Just now, dpmiller said:

PIR sensor/valve

 

How does that work? Microprocessor controlled?

Just now, Dreadnaught said:

 

Yes, nice solution. But I am aiming to avoid the extra complication of a hot return.

 

It's really not that complicated  - some 15mm pipe at the end of the wider bore distribution and a pump plus either a stat or switch.

 

1 minute ago, Dreadnaught said:

 

How does that work? Microprocessor controlled?

 

Nope, the sparky just daisy chained the relevant neutrals together and it all works - I have a more detailed explanation somewhere but it's very low tech and very effective.

2 minutes ago, Dreadnaught said:

 

How does that work? Microprocessor controlled?

 

No, just a wee battery powered low current valve, switched by a motion sensor.

 

this kinda thng, but I'm looking for one with adjustable timing. Most do two short pulses, some are variable

 

https://www.aliexpress.com/item/32848350151.html?spm=a2g0o.productlist.0.0.4fe43820q2WQ3f&algo_pvid=1cbe2c9a-6d06-4c72-850b-1f700474f92a&algo_expid=1cbe2c9a-6d06-4c72-850b-1f700474f92a-46&btsid=2100bdd816117404856013770e9c73&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

This looks good as a possible solution (and doesn't look hideous): https://www.washroomhub.co.uk/dvs-ac02-023-wall-mounted-brushed-stainless-steel-urinal-sensor-c-w-2m-extension-cable, £125. But seems to need an expensive handheld controller to program it (£250). 

 

This discussion also makes me think of sensor taps too. Anybody installed those?

2 minutes ago, dpmiller said:

No, just a wee battery powered low current valve, switched by a motion sensor.

 

Battery powered – is it not allowed to have a mains version in a bathroom I wonder? 

It needs to be more sophisticated.  Purge the line upon detecting occupancy, but stop as soon as hot water is detected with a pipe temperature sensor, so it won't purge the pipe if you come back in and it is still warm.

 

A perfect boffins job using an Arduino or the new micro pi (forget it's correct name)

transformer on the other side of a wall would be fine

you build it @ProDave, we'll fit it...

23 minutes ago, Dreadnaught said:

 

True, although I was told that Geberit cisterns, which I am choosing, are insulated anyhow.

 

They are : body made of Tupperware and there's a poly WhatEverItIs envelope round that. Warm enough to keep our tropical fish in. 

3 minutes ago, ProDave said:

...

A perfect boffins job using an Arduino or the new micro pi (forget it's correct name)

 

Be good to have the boffin back wouldn't it? My God, can you imagine him getting his teeth into this one.......

With such an Ali-Express-type PIR-flush-valve, where would the water discharge? 

 

I imagine it would go down its own drain connection, not visible (and audibly) out-of-the-tap and down the sink. 

 

Its an ingenious solution.

 

 

Edited January 27, 20215 yr by Dreadnaught

1 hour ago, Dreadnaught said:

If the bathroom is a long way away from hot-water source, I recall a post where @PeterW suggested connecting the hot pipe also to the WC cistern so that flushing the toilet would pull through the dead-leg of cold water in the pipe. (I searched but could not find the old post.)

 

Is this still considered a good idea?  My bathroom will be about 15m from the hot-water source (a Sunamp).

wasn't me .... but someone did suggest it ..!

22 minutes ago, dpmiller said:

a wee battery powered

Is that a WC related pun ..? ?

not a wee pun, just a wee Ulsterism.

 

@Dreadnaught I anticipate running it's drain into the basin drain through a clamp-on appliance tapping

https://www.bes.co.uk/single-self-cutting-washing-machine-waste-6957/