Valiant anti cycling function

[Diana1990]

Hey all

New here and would like to some advice and help. Always lived in properties with ideal boilers. I moved this year and current property had a valiant boiler installed in 2022. Have used the heating only handful of times as it been mild. Can someone please explain exactly what 'Anti cycling function' is? My valiant boiler displays this hour glass symbol flashing on the my display screen. After googling I still none wiser what the purpose is because while this is displaying it's seems there no heat to my rads, thus they cool down until this function stops. Sounds utterly ridiculous and this function is usually in effect for 15mins or so. Can the time be altered? No idea what it's for really and it's purpose...

 

[Johntheo5]

All boilers have a minimum output, if your heating demand is, or falls lower than this, then the boiler flow temperature will start to increase and when it exceeds the targettemp+5C then the burner will trip but the circ pump will remain running, when the anticycle time has elapsed and providing the flowtemp is < targettemp-5C then it will refire, the reason why it must have a anticycle time (and not just refire at targettemp-5C) is because all boilers fire up at ~ 60% of their rated max output and will not start to modulate until targettemp is reached, if the flowtemp on refiring is only 5C less than the target temp then the burner will trip every time because it will very quickly exceed the targettemp+5C.
You need to get the flowtemp down by ~ 15C or more before refiring, some boilers have a fixed anticycle time of maybe 3 to 5 minutes but Vaillant have a settable anticycle time based on the table attached. IF your targetemp is 65C, look at the maximum burner anti-cycling time (min) across the top of the table and where you see 20 (the default setting) look vertically downwards on this column until it meets the 65C row from the left, where these intersect is the actual anticycling time of 4.5 minutes, if the boiler is repeatedly going into recycle then you may have to increase this default setting of 20, to say 35, which will give a longer recycle time of 7.0 minutes, (thats IF the target temp is 65C)

What model Vaillant do you have and what is the targettemp set to?.

 

[Diana1990]

Thanks for the reply.

Target temp, you mean the flow temp of my radiators? Set at 65c

 

[Diana1990]

Fyi have Eco fit pure 825

 

[Harry Bloomfield]

Target temp, you mean what the thermostat control is set at? I'm sorry, I don't particularly understand. All I understand is that when my heating is on (roughly 2hrs, the anti cycling function happened 3 times and last about 15mins, during which times it seemed my rads fooled down)

It is the target temperature, of the water flowing out of the boiler itself. If the boiler cannot get rid of the heat effectively, by modulating down to minimum heat output, then, if there is still a demand for heat, it will have to enable the anti-cycling. How long that is enabled for, can be changed, but is listed in that download.

Your radiators, partially blocked, will possibly be causing the anti-cycling to be more obvious, as well as cause it to happen more frequently. If some radiators are partially obstructed, then it might be worth looking at others, and checking the pipework.

 

[Diana1990]

It is the target temperature, of the water flowing out of the boiler itself. If the boiler cannot get rid of the heat effectively, by modulating down to minimum heat output, then, if there is still a demand for heat, it will have to enable the anti-cycling. How long that is enabled for, can be changed, but is listed in that download.

Your radiators, partially blocked, will possibly be causing the anti-cycling to be more obvious, as well as cause it to happen more frequently. If some radiators are partially obstructed, then it might be worth looking at others, and checking the pipework.

I think I'm starting to to understand now. I editted my post. My flow temp of my rads is currently set at 65c. Only one is partially blocked, all my rads are getting totally replaced next week, part of my list of doing up myself place lol. All other rads were bled prior to using the heating and all heat up evenly. It's just that one radiator. I suspected this was adding to the issue. So I can alter the maximum cycling time. I managed to figure out out to get into this setting, it's on the default setting of 20mins. To lower the time the anti cycling function is in effect, I can adjust it down to say 10mins right?

 

[Harry Bloomfield]

So I can alter the maximum cycling time. I managed to figure out out to get into this setting, it's on the default setting of 20mins. To lower the time the anti cycling function is in effect, I can adjust it down to say 10mins right?

Yes, but it might mean slightly increased wear and tear on the boiler, and slightly increased gas usage, the shorter the timing is set for.

 

[Diana1990]

Yes, but it might mean slightly increased wear and tear on the boiler, and slightly increased gas usage, the shorter the timing is set for.

So, even though it states 20mins on boiler, it doesn't actually mean it's on the anti cycling function for full 20mins? Going by that chart, flow temp on rads/boiler set at 65c... Looking across under the max setting of 20mins is 4.5mins so that's technically how long my boiler is stuck on this function, and to get this right during this cycle is there no heat tod my rads?

Is valiant the only boiler that do this? I had Ideal boiler at last house and never spotted anything like this. My rads never ever cooled down unless the temp on thermostat was hit.

 

[Johntheo5]

I think I'm starting to to understand now. I editted my post. My flow temp of my rads is currently set at 65c. Only one is partially blocked, all my rads are getting totally replaced next week, part of my list of doing up myself place lol. All other rads were bled prior to using the heating and all heat up evenly. It's just that one radiator. I suspected this was adding to the issue. So I can alter the maximum cycling time. I managed to figure out out to get into this setting, it's on the default setting of 20mins. To lower the time the anti cycling function is in effect, I can adjust it down to say 10mins right?

A default setting of 20C with a target temp of 65C gives a actual anticycle time of 7minutes, if the boiler is repeatedly cycling before finally getting away then that suggests that the anticycle time should be set higher but that max settable time is 60 minutes which at 65C is a actual anticycle time of 11.5 minutes, so wonder why is it waiting for 15 minutes, you have checked that d.02 is set to 20 in the diagnostic codes?

And yes, all gas boilers have a anticycle time, but Vaillants can be a right pain as they (or used to) hold the ignition settings for up to 60 secs before allowing modulation, most other boilers allow modulation within 10 secs or so.

 

[Diana1990]

Yes, its set at 20mins currently. That's the default setting for it which suggests it's never been changed. My heating, I've used it perhaps 4 times so far, and each time (heating on roughly 2.5hrs) this function I spotted happened 3 times roughly (during each time my heating was on) . I can't tell if this is normal or not. My rads cool down ever so lightly during until the cycling stops. The temp in my house doesn't drop at all so the heat holes, but I just thought this is counter active because rads are coming down, so it then had to reheat it again. Makes no sense sense to me. I'd rather the cycling function is on for least amount of time. But given what been said, shall it leave it set at 20mins.

Regarding previous cycling times, I estimate it to have been for 15mins, perhaps less. But my flow temp then was set at 50c. I've since turned it up but haven't used my heating since I turned the flow temp up.

 

[Johntheo5]

Correction, I said above that 65C/20mins = anticycletime of 7mins but as you correctly said its 4.5mins, 50C/20mins gave 9.5secs, running at 65C now should help as the boiler output required will be higher so maybe less time that its minimum output is > the heating demand, if it does go into anticycle a number of times try and see the flowtemp just before it refires, you may have to increase the anticycle time get the flowtemp lower to allow the boiler to get away after one cycle.

 

[Diana1990]

It's rather mild where I am currently, so don't foresee heating on anytime soo. But next I use it I will keep eye and see what the flow temp is before it refires. I don't understand though why to Increase the the anti cycle time? Shouldn't I decrease it to say 10mins?

 

[Johntheo5]

No, you may need to increase it to get the flowtemp lower before the boiler refires to avoid it reaching 70C and burner trip, your anticycle time is now only 4.5mins at 65C/20C. Setting it to 35 will give a anticycle time of 7mins which may be required, or more, especially since there may be some resistance to the flowrate.

 

[Diana1990]

No, you may need to increase it to get the flowtemp lower before the boiler refires to avoid it reaching 70C and burner trip, your anticycle time is now only 4.5mins at 65C/20C. Setting it to 35 will give a anticycle time of 7mins which may be required, or more, especially since there may be some resistance to the flowrate.

But then 7mins.... That's enough for rads to rapidly cool down as it not currently circulating the water to the rads.

Does all this indicate something could be wrong? My plumber will be here next Tuesday so he'll service at same time. But is there anything I should bring up? I know this function is standard and is meant to happen, but is it something that should always happen everytime there is heating on?

 

[Johntheo5]

The circ pump keeps running in anticycle mode so yes the rads will cool down rapidly (burner bot firing) but will still emit some bit of heat until the burner refires, one period of anticycling won't reduce the room temps by much but multiple cycling certainly will.

Boiler going to recycle in itself doesn't mean anything is wrong, it simply means that the heating demand is lower than the boiler's minimum output, it may help (when refiring after a anticycle period) to reduce the maximum boiler output (this does not affect the boiler output in DHW mode) by adjusting d.02 to what you think is your maximum rad output in kw, can be calculated ~ by number of rads, size, single or double panel etc. Do you have zoning or/and thermostatic rad valves, TRVs, ??

You might care to fire up your boiler today or sometime before your plumber arrives and note d.40&d.41, flow&return temps after the system is up to temperature, say 20 minutes or so, if the flow&return temps have a big dT, say 25C or so, then indicitive of restricted flow due to sludge build up etc.
Also note d.15 pump speed, so d.15, d.40, & d.41