Anti cycling

[Dan Robinson]

A bit like saying:

" I understand how a shoelace is tied, what I don't get is why you tie a shoe lace".

Think of a car. It has a minimum RPM of usually 800 before the engine has to switch off/stall.

Boiler is the same..,. Although the minimum varies greatly between different units for reasons we won't go into here, if only to keep Blowhardgreen in his box.

Boiler is set to 70 degrees.

When the system water reaches 70 degrees, the boiler tries to lower the amount of gas burned (its RPM) to keep the engine running that bit longer.

IF it can't, then it switches off but leaves the pump running to dissipate the heat usefully.

To prevent the boiler yoyoing on and off, there is a program built in to minimise/maximise various things like MTF, efficiency etc.

Some boilers let you tweak the parameters, others do not.

This is the basics. There are all sorts of other things that can effect it, but the above will cover 90% of installations.

 

[mrshr]

Ok what I'm saying is, I get that there's a count down timer initiated and needs to elapse before the boiler will fire up again; and that the period during this countdown occurs is labelled anticycling mode.

What i don't get is why does the boiler enter this state in the first place.
Why doesn't it just carry on burning if there's still a call for heat?

 

[scoobydo123]

Because the flow temp has exceeded the set point because the boiler cannot modulate down any further. Every modulating boiler has a turn down ratio some go much lower than others.

 

[mrshr]

Boiler is set to 70 degrees.

When the system water reaches 70 degrees, the boiler tries to lower the amount of gas burned (its RPM) to keep the engine running that bit longer.

IF it can't, then it switches off but leaves the pump running to dissipate the heat usefully.

To prevent the boiler yoyoing on and off, there is a program built in to minimise/maximise various things like MTF, efficiency etc.

Some boilers let you tweak the parameters, others do not.

This is the basics. There are all sorts of other things that can effect it, but the above will cover 90% of installations.

So surely the boiler could sense it's about to stall and then up the gas accordingly?

 

[scoobydo123]

Have you not read my post? Starting to think this might be a wind up. What is the boiler make and model?

 

[mrshr]

Have you not read my post? Starting to think this might be a wind up. What is the boiler make and model?

You responded whilst I was entering my last post, so no I hadn't seen it at the time of writing.
Val 637

 

[scoobydo123]

So are you actually getting cycling or just asking about it?

 

[Dan Robinson]

So surely the boiler could sense it's about to stall and then up the gas accordingly?

It is the other way round.

 

[mrshr]

So are you actually getting cycling or just asking about it?

I'm getting it a lot.
Just been reading a bit about modulation ratios. Mine probably doesn't go very low.

 

[scoobydo123]

does it a lot when? On CH demand or DHW? How many radiators have you got and what is the insulation like of your house. What HW cylinder do you have? What is the tank stat set to? We are now getting somewhere

 

[Dan Robinson]

there's a count down timer initiated

Not necessarily.

 

[Dan Robinson]

Boiler is?

 

[mrshr]

Ok so I now have vsmart as my controller.
22 rads all on one zone.
Megaflo 250 l cylinder.
Loft insulation excellent, cavity walls ok.

Cycling occurring on CH.
Here's a scenario:
Outside temp 12 degC
Inside temp 20 degC
Target temp 21 degC

So, as inside temp is close to target temp (only 1 degC away) vsmart tells boiler to set boiler flow to only 43 degC. Boiler starts to heat flow water and before long it hits 43 and then boom, we're in anti cycling mode. Rads barely get warm and house will never reach target temp. Boiler just bouncing on and off.

There are two ways around this:
1) crank the desired temp up to say 25 degC. This causes vsmart to demand a higher flow temp. Plus I have to turn down desired temp once house warmed up.

2) Crank the vsmart heating curve up really high so it demands a higher flow temp.

But both of these work arounds are inefficient which goes against the point of having smart weather comp kit.

I'm asking all these questions as I'm trying to determined how to get the sweet spot of efficient energy consumption and comfortable living environment.

 

[mrshr]

Boiler is?

Vaillant 637
I believe these have a count down timer that can be altered, based on temperature.

 

[Dan Robinson]

Set d.0 to 18.