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Flow temp vs power rating
- Thread starter John Smith Esq.
- Start date
Re the bold highlight.
If the boiler ran for 7 minutes and over, it would (in theory) have no time left for the anti cycle when it hit the Flow Set Point (FSP)+4 (usually on a Worcester). so it would then cycle on the hysteresis you have set (-12) I think you said.
To test, put your boiler flow to 45c, anti cycle to 7 mins and hysteresis to -3, on the first run the boiler should be on for over 7 minutes. It will then hit 45c+4 =49c, it will then start dropping using the hysteresis as it has no anti cycle time to use and will not refire until -3 is hit. This shouldn't be too long. Think about it, if it has no anti cycle time left what does it use? The temp hysteresis ! Took me ages to figure this out so you're not alone. The wife thought I was going barmy timing the boiler fires
Anti cycle time is TOTAL on/off time minimum.
EDIT: This I'm not certain about now.
On the other hand, using the settings as above, if the boiler ran for 5 mins in total after hitting FSP+4 it would then be off for only another 2 minutes (7 minutes specified anti cycle time), wether it hit the hysteresis drop or not.
Last edited:
Re the bold highlight.
If the boiler ran for 7 minutes and over, it would (in theory) have no time left for the anti cycle when it hit the Flow Set Point (FSP)+4 (usually on a Worcester). so it would then cycle on the hysteresis you have set (-12) I think you said.
To test, put your boiler flow to 45c, anti cycle to 7 mins and hysteresis to -3, on the first run the boiler should be on for over 7 minutes. It will then hit 45c+4 =49c, it will then start dropping using the hysteresis as it has no anti cycle time to use and will not refire until -3 is hit. This shouldn't be too long. Think about it, if it has no anti cycle time left what does it use? The temp hysteresis ! Look me ages to figure this out so you're not alone. The wife thought I was going barmy timing the boiler fires
Anti cycle time is TOTAL on/off time minimum.
On the other hand, using the settings as above, if the boiler ran for 5 mins in total after hitting FSP+4 it would then be off for only another 2 minutes (7 minutes specified anti cycle time), wether it hit the hysteresis drop or not.
I wouldn't have thought that the boiler run time would have any effect on the anti cycle time.
On Vaillants the actual anticycle time depends on the set anticycle time and the target flow temperature, if the boiler is set to its default anticycle time of 20 minutes, then a target temperature of 65C will result in a actual anticycle time of 4.5 minutes, 20C+65C gives a actual anticycle time of 6.0 minutes etc. The anticycle hysteresis is a non settable 5C. It doesn't matter how long the boiler fires for, it could be firing for hours on end when say a zone is turned off and the heat demand may then fall below the boiler's minimum output, if so, when the flow temperature reaches the target temp + 5C, the burner will trip, the circ pump continues to run, the burner will then refire when the anticycle time has elapsed IF the flow temperature is target temp -5C, if the flow temperature is greater than this then the burner will not refire until it falls to target temp - 5C, it most certainly will not fire when/if the flow temp reaches target temperature - 5C before the anticycle time has elapsed. If the boiler then only runs for 4 minutes and the burner again trips at target temperature + 5C, then the same anticycle terms apply.
Boilers with adjustable anticycle hysteresis may refire when the flow temperature falls to target temperature - the set hysteresis??
Hi John
WB Greenstar Si boiler btw so it may be different.
The set point above flow temp is +4 (non adjustable)
I've timed cycle runs John, 2 on/off runs and they both totalled exactly 10 minutes, so I'm sure it's not coincidental
On first run I had set 2k anti hysteresis to test my theory
After hitting FT+4, boiler flow dropped 2c in under a minute (not surprisingly) and restarted, which then ran for 1.30 minutes before hitting FT+4, boiler went into ACT for 8.30 mins, then re fired and ran for over 13 minutes as the FT was a reasonably low level now.
It did this again in another test too, just to make sure I had it right.
THIS is the part I'm unsure of and can't get the scenario to test it :
Boiler fires, now if it runs for say, 8 minutes, will it then stay off for another 2 mins or will it wait to drop to 40c (the Anti Hysteresis of -6) before firing again ?
I would have thought, like you, that it would stay off until the AH has been hit (as it won't have dropped to that in 2 minutes), but, I'm sure (not certain, come to think of it now) that it only stays off for the ACT remainder of 2 minutes.
Settings
FT flow temp 46c
ACT anti cycle time 10 mins
Anti Hysteresis -6k
It does seem to me that the hysteresis only comes into effect if there is no ACT to use, therefore guaranteeing a temp drop on the flow.
Thoughts?
WB Greenstar Si boiler btw so it may be different.
The set point above flow temp is +4 (non adjustable)
I've timed cycle runs John, 2 on/off runs and they both totalled exactly 10 minutes, so I'm sure it's not coincidental
On first run I had set 2k anti hysteresis to test my theory
After hitting FT+4, boiler flow dropped 2c in under a minute (not surprisingly) and restarted, which then ran for 1.30 minutes before hitting FT+4, boiler went into ACT for 8.30 mins, then re fired and ran for over 13 minutes as the FT was a reasonably low level now.
It did this again in another test too, just to make sure I had it right.
THIS is the part I'm unsure of and can't get the scenario to test it :
Boiler fires, now if it runs for say, 8 minutes, will it then stay off for another 2 mins or will it wait to drop to 40c (the Anti Hysteresis of -6) before firing again ?
I would have thought, like you, that it would stay off until the AH has been hit (as it won't have dropped to that in 2 minutes), but, I'm sure (not certain, come to think of it now) that it only stays off for the ACT remainder of 2 minutes.
Settings
FT flow temp 46c
ACT anti cycle time 10 mins
Anti Hysteresis -6k
It does seem to me that the hysteresis only comes into effect if there is no ACT to use, therefore guaranteeing a temp drop on the flow.
Thoughts?
Me? No...
Perhaps something you might want to look at to save a bit of manual tweaking
I don't think it's available for my boiler 2014 WB Si Compact, according to WB Tech. anyway
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Thanks for your comments. I see I'm not the only one who has been fiddling around with settings in an obsessive way and had the missus wondering what it's all aboutRe the bold highlight.
If the boiler ran for 7 minutes and over, it would (in theory) have no time left for the anti cycle when it hit the Flow Set Point (FSP)+4 (usually on a Worcester). so it would then cycle on the hysteresis you have set (-12) I think you said.
To test, put your boiler flow to 45c, anti cycle to 7 mins and hysteresis to -3, on the first run the boiler should be on for over 7 minutes. It will then hit 45c+4 =49c, it will then start dropping using the hysteresis as it has no anti cycle time to use and will not refire until -3 is hit. This shouldn't be too long. Think about it, if it has no anti cycle time left what does it use? The temp hysteresis ! Took me ages to figure this out so you're not alone. The wife thought I was going barmy timing the boiler fires
Anti cycle time is TOTAL on/off time minimum.
EDIT: This I'm not certain about now.
On the other hand, using the settings as above, if the boiler ran for 5 mins in total after hitting FSP+4 it would then be off for only another 2 minutes (7 minutes specified anti cycle time), wether it hit the hysteresis drop or not.
That's useful to know about the flow temp +4C on a Worcester. Explains why it wasn't getting to 5 above as I was expecting.
In terms of my current settings. I have flow temp set to 60C, anti fast cycle flow temp (K) -14, and anti fast cycle time 15 mins.
My thinking is that once the flow temp +4 is reached, let it turn off for a bit (until 14C below flow temp reached or 15 mins elapsed - assuming one of these triggers it back on), then let it run through a longer burn from a lower temperature, for more efficient heating.
Is my logic correct? Do these settings seem reasonable?
Your logic is correct.Thanks for your comments. I see I'm not the only one who has been fiddling around with settings in an obsessive way and had the missus wondering what it's all about
That's useful to know about the flow temp +4C on a Worcester. Explains why it wasn't getting to 5 above as I was expecting.
In terms of my current settings. I have flow temp set to 60C, anti fast cycle flow temp (K) -14, and anti fast cycle time 15 mins.
My thinking is that once the flow temp +4 is reached, let it turn off for a bit (until 14C below flow temp reached or 15 mins elapsed - assuming one of these triggers it back on), then let it run through a longer burn from a lower temperature, for more efficient heating.
Is my logic correct? Do these settings seem reasonable?
First off, the anti cycle time (on a Worcester) is the TOTAL minimum time on/off.
E.G On the first fire up the boiler will easily run the anti cycle time you set of 15 minutes, therefore when it reaches SP +4 (Boiler flow temp +4), it won't have any anti cycle time to use up, so it will revert to the anti hysteresis that you set (-14), the -14 btw is from the initial SP, so, it will wait until the boiler shows 46c (60-14) and then fire up (providing your room stat temp hasn't been reached. Now, if the temp drop isn't enough and say it runs for 10 minutes, in theory it would have 5 minutes of anti cycle time left, BUT because (hopefully) it takes longer to reach -14, then the boiler will wait again.
On the other hand, say you set the anti hysteresis at -4 (which would take seconds to cool on a 60c temp), if the boiler ran say for only 10 minutes, then, because the anti hysteresis of -4 would have been reached in seconds, then it WILL wait until the remainder of minutes is spent, as it is longer.
What I've done (or am trying to do) is control the boiler cycles via the anti hysteresis only, so I've set the anti cycle time to 5 minutes, as it will easily run for 5 minutes, but set the anti hysteresis to -9 on a 50c flow (the flow temp has to then drop to 41c), this roughly equates to an off time of around 8 or 9 minutes and then allows the boiler to run for 10 to 15 minutes and this usually is enough time for the room stat to be satisfied.
So,
Initial fire up, 30 to 45 minutes (depending on outside/indoor temp), sometimes this satisfies the daily room 18c temp but if not, the boiler flow temp rises eventually to 54c, it then goes into the anti hysteresis (code 204, anti cycle time code is 202, 200 is boiler firing and 203 is boiler satisfied), and goes through the sequence in the paragraph above.
This way, I don't need to control 2 variables (anti cycle time and anti hysteresis).
I'd time how long before it reaches -14 in you case, too long and you could be literally waiting 30/40/50 minutes and above but too short and the temp is too high on re firing and therefore reaches the flow temp +4 too quickly.
I hope this explains a little, as, like you, I thought the anti cycle time was the time it WAS OFF after reaching flow temp +4, it's not it's waiting time IF there's any left after each burn.
Hope this helps
In my edit on the previous reply of mine, I am now certain this is how it works, WB tech also replied in agreement.
So, if the (remaining) anticycle time is used up, the boiler will wait and not refire until the flow temp falls to SP temp - the set hysteresis? or
If the flow temp falls to the SP temp - the set hysteresis before the remaining anticycle time is used up then the boiler will wait and not refire until the remaining anticycle time is used up?
Is this how it works?.
If the flow temp falls to the SP temp - the set hysteresis before the remaining anticycle time is used up then the boiler will wait and not refire until the remaining anticycle time is used up?
Is this how it works?.
Yes, whatever is longest, NOT the first criteria that is hit. The boiler will show which criteria it is using via the code(s), 202 means it's using the anti cycle TIME and 204 means it is using the anti hysteresis. You will find it initially shows 204 and then if the criteria is not achieved then it will change the code to 202 i.e. there must be some anti cycle time remaining.
200 is boiler firing for c/heating
203 means boiler is in stand by or off
Obviously increasing the heating ON time will effect internal warmth most, it will be warmer for longer.
The emitters can only emit what goes in and the property can only absorb what it can until the thermostat indicates it's warm enough the turns the boiler OFF.
Increasing flow temperature will put hotter water into the emitter which means its heat up of the space will be faster. Increasing the power of the boiler will put more heat energy into the same amount of system water.
Both these excesses will increase the likelyhood of heat input being too fast and too great for the load over time (the amount of heat the property can absorb before a room or boiler thermostat says stop).
Both increase cycling, increasing setpoint reduces the likelyhood of the boiler operating in a condesing mode.
If you are able to, slow the pump speed and restrict the lockshield valves on the radiators to lengthen the time water spends in the emitter, try to widen the delta T across the boiler flow and returns and stretch the anti-cycle time if it is adjustable. Reduce the boiler setpoint as low as possible without compromising comfort.
A poorly insulated 1930's three bed semi will have a heat loss probably less than 9kW and that only when it's say -3°C outside which thankfully it rarely is.
You are running anticycle settings 5 minutes, -9C, (Flowtemp SP 50C), to run with a anticyle period effectively based on temperature control only?, see below.
If there is no remaining anticycle time then the anticycle period is only determined by the flowtemp falling to SP-hysteresis, if the (flowtemp) SP is set very low, say 35/40C ( like with WC) then depending on the hysteresis setting, the boiler will take a age, if ever, to refire?. Its a bit surprising that a maximum anticycle time (separate from the normal anticycle time) can't be set somewhere?.
If there is no remaining anticycle time then the anticycle period is only determined by the flowtemp falling to SP-hysteresis, if the (flowtemp) SP is set very low, say 35/40C ( like with WC) then depending on the hysteresis setting, the boiler will take a age, if ever, to refire?. Its a bit surprising that a maximum anticycle time (separate from the normal anticycle time) can't be set somewhere?.
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Hi John
Yes it takes around 9 minutes to drop to the anti hysteresis that I have set. If I set it any lower then yes it takes ages, but this way I’m guaranteed a drop no matter how long the boiler fires for.
The Valiant boilers anti cycle software obviously works differently
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