Drayton Wiser and Vaillant Boiler

[SgtFoley]

Hi

I have a cpl of question, but I'm also posting as this might help others trying to get Drayton Wiser to work properly with Vaillant (or other boilers).

Setup: ecotec plus 418, S plan, installing Drayton Wiser smart controls (currently 3 rad valves).
Problem: the boiler is short-cycling sporadically... it often comes on for a very short time (as short as 10 sec!).

After a lot of testing (and help from support) this is what I worked out:
The Wiser controller operates on 6 cycles/hour max (for a gas boiler; this is also the default on evohome, so seems standard).
The Vaillant Ecotec 418 has a default anti-cycle time which (at my flow temp) seems to clock around 8/9 minutes.

So, for example: Wiser requests heat (using TPI algorithms) for 5 minutes... at minute 5, demand switches off, boiler off and starts anti-cycling for 8 mins... so when Wiser starts the next cycle (from minute 10), for the first 3 minutes of demand the boiler stays off cos it's still anti-cycling. By the time the boiler fires, the demand turns off.

I know there are some Vaillant experts here...
Is the default anti-cycle time on the ecotec plus unusually long? (the d2 setting, according to other threads)
Can this be safely (for boiler life!) reduced to say half the current setting?

Is 6 cycles/hour acceptable for this boiler?

Or is there a 'minimum boiler on' time I can set (without interfering with HW safety cut-out) to avoid the extreme short cycles?

thank you!

 

[fezster]

I'm not certain on this, and don't have time to look it up, but I'd have thought that the Wiser switching off (because of TPI) would remove demand from the boiler and put it into pump overrun (S.7), whereas the boiler enters anti cycling mode (S.8) when there is still demand, but it is unable to dissipate the heat. Therefore, the scenario you described would not occur (except that the boiler may still be in pump overrun, which is also adjustable).

 

[SgtFoley]

Thank you fezster
Anti cycling seems to come on every time the boiler stops, not just when the return temp is high. Maybe this in itself is not normal... although it makes some sense if the idea is just to stop itself from restarting too soon?
From the manual (and a comment from Bunny on this forum), it looks like the anti-cycling time is a function of flow temp...
https://www.diynot.com/diy/threads/...anti-cycling-mode.210861/page-2#ixzz5YtlzCiD6

Wiser switching off does indeed put the boiler in pump overrun... but the little rad symbol on the display flashes continuously from this point (I believe this shows anti cycling). The code goes to S.8 straight after S.7 is done (I guess if it could it would show both codes).

 

[fezster]

Worth having a read of this blog and comments to understand the anti cycling better:

http://vaillantcyclingproblem.blogspot.com/2012/01/anti-cycling-mode-and-d2-parameter.html?m=1

I don't think s8 should be entered, provided the heat has been adequately dissipated with the pump overrun. Im sure someone more knowledgeable will know the exact criteria it uses to decide whether to go into s8 or not.

 

[SgtFoley]

Thank you
I had read that blog, but not to the end of the comments! (and the table doesn't load for me)

So I had the impression the anti cycling came on all the time; but I now see it should only come on based on the return vs flow temp diff.
If that's the case, that may well be my problem... my bypass loop was bolted on as an afterthought and is too short (installer cutting corners, I didn't do it myself).
This is going to cost me!

Thank you for your help!

 

[HKB]

My 24 year old Potterton boiler was short cycling after installing the Wiser system.

It sometimes fires up and the pump runs for only a few seconds. It also boils up and I suspect short pump times may not help, but this may be unrelated.

I initially suspected the overrun thermostat was faulty because of the odd switching on and off of the pump, but changing the overrun stat made no difference.

Closer attention revealed that the Wiser hub is calling for heat many times an hour and sometimes for well under a minute.

I called Drayton to ask about the strange beahvour and short cycling and they recommended I change the Wiser hub settings from gas to oil. Apparently the oil boiler option in the hub algorithm has a cycling limit.

I have now tried it and it is much quieter with no more random switching. It may be worth a try for the Vaillant.

 

[SgtFoley]

Hi hkb
Yes, that behaviour sounds familiar...

On "oil" setting wiser does 3 cycles an hour.
On gas it still calls for heat no more than 6 times per hour.

I also remember observing it and thinking it was stop-starting loads of times, but on closer inspection the 6/hour was respected... It just felt very frequent because the anti cycling was interfering and causing some very short on-off episodes.

 

[HKB]

Thanks. I haven’t counted. But the oil setting is a lot less intrusive. It seems to overshoot a little more, but only by 0.5C which is a small price to pay for a quiet life (and perhaps more efficient gas usage on an old boiler). I’ll never know because it’s not a controlled experiment. I would need a duplicate house to run that.

Now that I’ve read up more on Wiser, it seems the short pulses of heat calling are a deliberate part of the algorithm. But is it really more efficient to keep lighting a boiler? Or is it less efficient? If it habitually overshoots I can set the temperature a degree lower.

 

[Someuser08]

If it habitually overshoots I can set the temperature a degree lower.

What do you use for temperature with wiser - room or radiator thermostats?

 

[HKB]

So far only one room thermostat in a central downstairs location. The ground floor is semi-open-plan.

I’ve started cautiously. I may buy radiator stats later for some bedrooms.

 

[Someuser08]

You are not supposed to have overshoots in the temperature when room thermostat is used (unless its positioned completely wrong, like on external wall or by the window). Wiser learns how quickly a zone heats up and adjusts heating patterns to keep the required temperature exactly.

When you add radiator thermostats in a zone without a room thermostat then it becomes much more tricky as the temperature read will never be all that correct. For that reason I'm using radiator thermostats along with room thermostats with Wiser.

 

[HKB]

Not sure why, but it is overshooting by 0.5C.

Today it was calling for heat at one point even though measuring 20.5C with a set point of 20C. I hope it will settle down but I don’t know how adaptive or sophisticated the software is.

 

[Someuser08]

If you do not have radiator thermostats then precise control will never be quite possible. What my system does is opening valves very slightly to not allow radiators to heat up a lot when it maintains the temperature.

Of course if you are coming from a much lower temperature (overnight) then its easy to overshoot especially if you have large radiators carrying a lot of heat even after boiler has stopped. Other than that I have never seen mine to call for heat when temperature is above the set point.

One thing to note though - I'm not sure what calling for heat actually means in the app. I've noticed for sure that sometime it says its calling for heat but its not actually firing the boiler(but never the other way around). It could be that indicator is somehow using different algorithm to the control box itself...

 

[TolseyClock]

Very useful. Liked the tip to 'pretend' to be an oil boiler.
I too objected to the fast short cycles so I simply set the Wiser to OpenTherm. OK, you get a warning - but the Wiser is now on or off based on demand with no cycling.
I have ordered an OpenTherm shield board for an Arduino and will convert my Vaillant by adjusting the boiler temperature based on the OpenTherm demand. Will post if I have success. Very pleased with the Wiser (and with my old Vaillant).

 

[TolseyClock]

Update : the Arduino OpenTherm
https://www.tindie.com/products/jiripraus/opentherm-gateway-arduino-shield/
worked really well. Drove a dummy 10k pot with a Futaba wired in parallel to the 10k central heating water temperature to create the demand voltage but you could belt drive the knob to avoid wiring to the PCBs.
Happy to share the Arduino code. You can either just relay the OT boiler temperature or customise it (which is what I've done).