Anti Cycling mode on hot water only

[mrshr]

So what are the issues of having an oversized boiler? (other than the cylinder thing discussed here.)

Presumable, the bigger boiler costs more to purchase and then to run too?

Are we essentially comparing a Corsa to Rolls Royce:

Both will get to 70 mph (or deg C!!) but the Corsa will be working quite hard to get there, yet the Roller will barely be breaking a sweat. The Roller also burns more fuel in doing what it does whereas the Corsa would be less expensive to run?
Fair analogy?

 

[Dan Robinson]

Your big boiler will be unable to stay in a nice efficient cruise and will starting and stopping more.

 

[mrshr]

I'm pretty sure I don't get the stop starting with my heating though.

 

[picasso]

Forget the heating side of your system, when you have hot water only the boiler can only modulate down to 12kw, that is the absolute minimum it can run at, when your hot water cylinder is nearing 60c the return will be too close to the flow temp (as the boiler is still producing 12kw) and it will shut down before it melts its self,

put your boiler on 75c set the cylinder stat at 55c and then leave it alone as you cant do much more.

 

[mrshr]

Forget the heating side of your system, when you have hot water only the boiler can only modulate down to 12kw, that is the absolute minimum it can run at, when your hot water cylinder is nearing 60c the return will be too close to the flow temp (as the boiler is still producing 12kw) and it will shut down before it melts its self,

put your boiler on 75c set the cylinder stat at 55c and then leave it alone as you cant do much more.

Agree with that, but I'm wondering what are the other drawbacks of having an oversized boiler.

Surely most people with a system boiler at some time or another only heat the cylinder. Are all of us with a system boiler having the issue I'm having?
For example, let's say that the heatloss calcs determined that a house needs a 37kW boiler, surely there will be times when that home owner only wants to heat the cyllinder and therefore will have this problem?

 

[mrshr]

put your boiler on 75c set the cylinder stat at 55c and then leave it alone as you cant do much more.

Aren't we supposed to set it at 60 deg C to kill off bacteria?[/b]

 

[picasso]

Its a compromise trying to stop your boiler cycling, I dont think there has ever been a case on legionnairs recorded in a domestic property (the idea behind the 60c) if your worried you can always turn the cylinder stat up once a week.

 

[Dan Robinson]

Most people just live with boiler cycling.

That's why I love installation work that I get to design and don't meet the customer until the end, or sometimes even a year after completion

Got three on the go like that at the moment. Blooming marvellous.

 

[St0rmer66]

put your boiler on 75c set the cylinder stat at 55c and then leave it alone as you cant do much more.

Aren't we supposed to set it at 60 deg C to kill off bacteria?[/b]

Anything above 50 is safe enough unless you leave it sat there with no water drawn off for months at a time. I would say 90% of the customers I come across have their cylinder at 50-55 degrees because 60 scalds your hands! (especially children and the elderly).

 

[Onetap]

put your boiler on 75c set the cylinder stat at 55c and then leave it alone as you cant do much more.

Aren't we supposed to set it at 60 deg C to kill off bacteria?[/b]

Yes, according to the HSE (L8, Control of legionella in water systems). Store at 60degC.

The thermostat/temperature sensor is usually about 2/3rd of the way up the cylinder and the legionella colonises the colder water at the bottom of the cylinder amongst all the limescale that has accumulated. The water will also be cooler at the end of the distribution system. If it's warm enough to wash your hands, it is too cold. Fit TMVs if children, disabled or elderly people use it.

Elderly people complain if they scald their hands. They don't complain much when they croak quietly in hospital from pneumonia due to an infected water system.

And yes, domestic systems do harbour legionella.

And no, the HSE won't bother testing it because the H&S at Work legislation doesn't apply to houses.