Combi DHW startup times

[dilalio]

It's the Internet of things!

 

[bernardgreen]

It's the Internet of things!

As in when the fridge packs up it e-mails the boiler to ask for lower room temperatures to delay the event that the food starts to warm up.

 

[Dan Robinson]

What does it do on Monday when every one is at the office having had all the family staying for the weekend and using lots of hot water

You might waste 2p of gas. Shock horror. Let's all bin the concept of combination boilers don white socks and sandals and contrive stone needlessly complicated bespoke system to have a shower and heat a whole cylinder of water to run it.

You have to be joking, "sorry you can't have this boiler unless you also have a smart phone

If you don't own a smart phone you are unlikely to be interested in geofencing.

That does seem to be a long time, is that your estimate or is it actual recorded data

It's a educated generalisation based on actually knowing what I'm talking about, and his boilers work.

In reality aren't these predictive controls little more than a gimmick

It's an evolution in control As with everything it has its uses. I have a client who is a freelance personal tour guide. She lives alone and works completely random hours and across Europe... Geofencing her Heating was a revelation and saved her a fortune.

Stop pontificating for Christ's sake.

 

[Dan Robinson]

Try a CombiSave on the DHW outlet. It restricts the water flow until the DHW temperature is up to setpoint temp then opens fully. It saves gas and water. About £48. But open the tap with a slight flow until up to temp, then when hot open fully - and save £48. Having a manifold with 10mm pipe to each tap will make matters better as well - less water in the dead leg pipe.

I relive a Potterton had a device to restrict the flow until up to temp.

It was the Puma.

The combisave device is not reliable.

 

[ericmark]

I know my boiler has an Eco button, without it being activated there is a small store of hot water held in the boiler, so water to tap is hot much quicker, and you still get hot water with a reduced flow. If the Eco button is activated then hot taps need to be full on for boiler to fire up and there is a delay getting hot water.

So in the main may cost a little more because boiler fires up to keep water store hot, but it in the main saves water as no need to run off cold water.

The is one exception, the shower, without Eco activated the shower goes hot, then cold, then hot again as you use the reserve before the boiler it running long enough to replace it.

We found for some reason the tap very close to the boiler in kitchen would often fail to activate the boiler when turned on in Eco mode, so we turned off Eco mode.

 

[durhamplumber]

No matter how super duper sophisticated your preheat is,you still have the deadleg between boiler and tap to run off

 

[bernardgreen]

to have a shower and heat a whole cylinder of water to run it.

( for new readers ) The cylinder also provides low pressure hot water for wash basins and bath. Also warms the airing cupboard.

 

[endecotp]

It would take some pretty impressive technology to correctly guess what time I’m going to get up in the morning.
Though a GPS tracker that knew what time I’d left the pub the night before might have a chance.

 

[muggles]

( for new readers ) The cylinder also provides low pressure hot water for wash basins and bath. Also warms the airing cupboard.

How very 1980s

 

[bernardgreen]

How very 1980s

Nothing wrong with life ( and plumbing ) in the 1980's

 

[hard-work]

I know a guy who was fed up with having cold water at the basin tap having a long dead-leg pipe. He put an instantaneous electric single point water heater under the basin fed from the hot draw-off pipe. He got quick hot water, then when hot water came through from the cylinder the electric heater would switch out. It worked out cheaper in installation and extra gas consumption than having a DHW primary loop. His DHW draw-off went via the basin and down to the kitchen. So the one electric unit did both. But not as quick in the kitchen as in the bathroom, but still a lot quicker.

 

[endecotp]

He put an instantaneous electric single point water heater under the basin fed from the hot draw-off pipe.

Instant or small tank heater? I was considering the latter, but you mention the former.

I have thought about that arrangement, but I’ve noticed that the instructions generally seem to say “for cold mains water only” or similar.
With an instant heater, I would be unenthusiastic about feeding in water at 60C and heating it to 95C and relying on its over-temp cutout to switch it off. With something like a 2kW 15l tank I’d be happier since its thermostat is part of its normal operation, not just a safety cutout.

 

[hard-work]

Instant or small tank heater? I was considering the latter, but you mention the former.

I have thought about that arrangement, but I’ve noticed that the instructions generally seem to say “for cold mains water only” or similar.
With an instant heater, I would be unenthusiastic about feeding in water at 60C and heating it to 95C and relying on its over-temp cutout to switch it off. With something like a 2kW 15l tank I’d be happier since its thermostat is part of its normal operation, not just a safety cutout.

I can't recall the make. It was instant and had a run stat and overheat as well. It did accept hot water into the inlet.

 

[foxhole]

You can get combi's which also have small storage unit , so if used little and often water is hot almost immediately.

 

[DP]

Dear Experts,

Do any combi manufacturers ever specify their hot water start-up times, from turning on the tap to hot water leaving the boiler?

It seems to me that this is one of the more important considerations, but I’ve never seen it quantified in the promotional blurbs or instruction books. Not that I have looked at many. Maybe they are all equally bad.

Boilers with preheat will deliver water right away
Mind you, important factor is how far away the draw off point is.

Combi boiler with preheat will have a small quantity of hot water ready for use to give boiler chance to come up to speed.