Vaillant boiler always exceeds set temperature

[kilodelta]

Hello. I have a Vaillant EcoFit boiler that is a few years old. We had our annual service last month and ever since then I’ve noticed something unusual.

The radiator mode temperature is set to 65C but it always exceeds that, hits 70C, and then stops and the the egg timer comes on. If I check the boiler status, I see either S.07 (pump overrun) or S.08 (anti cycling mode).

Is this normal? I called the engineer and he said it was. I’ve noticed the egg timer would sometimes come on if the Nest turned the heating on and off in quick succession, but not every time it fires up.

Thanks.

 

[V1ks44]

Suggest changing the Kw from Auto to 6kw, also the anticycle time d.002 might have to be increased from its present settiung of 20 mins, you should see a table somewhere that gives the actual anticycle time as it looks at the target flow temp and the set anticycle time to give the actual time.

Would doing this have any negative impact on the boiler?

Attaching the photo of the table for anticycle times, so at 60c as set currently would it be?

 

[ShaunCorbs]

Works out to around 6 kw on the ufh maybe

You want a difference of 7 degrees between flow and return on each circuit when warm so alter the flow meters to achieve this if you can

 

[John.g]

No, it shouldn't, 60C+20C(time) = anticycle time of 6 minutes, 60C+25C=7.5minutes & 60C+30C=9minutes.

I would increase that (d.002) initially to 25, a 7.5 min anticycle time, as it might reduce the starting temperature low enough to get the boiler away without exceeding the target temperature.

 

[V1ks44]

Works out to around 6 kw on the ufh maybe

You want a difference of 7 degrees between flow and return on each circuit when warm so alter the flow meters to achieve this if you can

yes thats what i have been trying recently to get, i dont know what my return temp are to be honest is there a way to check this?

when i checked the diagnostic menu on the boiler d.41 (i think it was) it was showing me like 55c, im not entirely sure if this is the return from the manifold or the whole system? as it seemed very high because when i touch the return copper pipe (one on the left in the pic i uploaded) its not very warm even when the UFH has been on for few hours. it could be due to the way the pipes are laid (single serpentine).

I dont have a temp gauge on the return part of the manifold, im certain the difference is higher than 7c because the UFH pipe layout is Single serpentine (this was a total mess by the plumber who did it and i didnt know anything about ufh at the time to correct anything). however i cant change this now so im just trying to find a way to get this best as i can. I will increase the flow rates and see if this changes.

What are your thoughts on the suggestion by John.g to change the boiler to 6kw and increase the Anticycle time. Im thinking to give this a try tomorrow morning and see how the system behaves...

 

[V1ks44]

No, it shouldn't, 60C+20C(time) = anticycle time of 6 minutes, 60C+25C=7.5minutes & 60C+30C=9minutes.

I would increase that (d.002) initially to 25, a 7.5 min anticycle time, as it might reduce the starting temperature low enough to get the boiler away without exceeding the target temperature.

Thanks John.g - i will give this a try tomorrow morning and report back.

I know a buffer tank is an option but i just dont have space near the boiler to fit this as this would solve the anticycle issue and allow the boiler to run in fully condensing mode.

 

[ShaunCorbs]

Clip on thermostat is the best tbh

Depends on the load as if it’s set right atm 3lpm you have 6kw on just the ufh without the rads

Tbh combi boiler or system eg hot water tank ?

 

[V1ks44]

Clip on thermostat is the best tbh

Depends on the load as if it’s set right atm 3lpm you have 6kw on just the ufh without the rads

Tbh combi boiler or system eg hot water tank ?

ok will try that...I have a system boiler Vaillant 637 with Horizontal 180L Unvented tank which is next to the boiler.

.someone suggested the below Actuators to me...they maintain the 7c difference (they have some clips on the which u attach to flow and return pipes on the manifold) and i can just leave all the flow meter fully open ...not sure if anyone on here has heard of them or any experience...they are around £20 each + del so not massively expensive...thought id share it as its in my list of things to try.

Salus Actuator – Auto Balance & Energy Saving​

 

[John.g]

I think the min output of that boiler is ~12kw so the boiler will probably cycle anyway on either with rads only on or UFH only on so the boiler temp must be got as low as possible before refiring after a recycle.

 

[ShaunCorbs]

ok will try that....someone suggested the below Actuators to me...they maintain the 7c difference (they have some clips on the which u attach to flow and return pipes on the manifold) and i can just leave all the flow meter fully open ...not sure if anyone on here has heard of them or any experience...they are around £20 each + del so not massively expensive...thought id share it as its in my list of things to try.

Salus Actuator – Auto Balance & Energy Saving​

Tbh should be easy to do with a clip on temp meter

 

[V1ks44]

Tbh should be easy to do with a clip on temp meter

ok cheers, ill try that.

 

[ShaunCorbs]

7-10 is ok better with as close to 7 as you can get

 

[V1ks44]

7-10 is ok better with as close to 7 as you can get

ok let me increase the flow rates i guess to the max and get this clip thermostat and then ill report back after testing over few days. I will also reduce the kw to the minimum ( i think it showed me 6kw) but i will try 12kw first and see.

Thank you both for the prompt responses this evening.

 

[V1ks44]

Just reporting back...

So i changed the D.00 to initially 12kw and then tested both UFH only and CH and it was still going into Anti cycling mode, with the UFH it did it more frequently then it did with CH.

Then i changed the setting to 8kw and same result and this morning i dropped it even further to 6kw and also dropping the Flow to 55C to see if this would have any impact. but still It went into anti cycle and the Flow would hot 65 before the change and then 60 so basically overshooting by 5c.

So today the UFH has been on longer due to kitchen being much cooler (also the -2/3 outside) than my living room, so what i noticed was at 6kw and 55C flow, the boiler would get to about 60c and then hit the anti cycle mode and then go down to about 40c, then it would stop complete when it got to 40c with the time only flashing (pump is not running at this 1-2 min period) and then will sit on this screen for about 1-2 min before firing again and going and heating to the desired flow temp.

I also noticed the return temp were above the desired 54c (needed for the boiler to be most efficient) regardless of the flow temp being at 55c, 60c or 65c.

I have come to a conclusion after reading various forums over the last 24 hours where there are may others on the same boat as me....THAT this is the best im going to get due to limitation in the setup i have, i believe the only way i can solve this is to have a buffer tank installed (as suggested by many others on various threads on the internet). But sadly i just dont have the space as i live in a terrace house with not much space to put one.

i assume with this usage the boiler wont be as efficient as one would like it to be but i dont see any other way...

@Shaun - i am still to find out the return temps on the loops, do you have suggestion on which clip thermometer i can buy? I have the attached Infra red guns but im not sure how accurate the readings are because when i did try it was giving much lower readings e.g. the incoming temp from boiler was 60C and when i pointed at the copper pipe just below the manifold as a test it would show 31c/ and then the flow pipes would on the manifold was showing 27c.

So i may get the clip ones you suggest - any recommendation?

 

[John.g]

How many rads?, have you tried it with both rads and UFH on together?, would also suggest increasing the flow temp to 65C and the anticycle time d.002 to 30mins, this gives a actual anticycle time of 6.5mins, if you do this then note that the actual time is 6.5 minutes when it goes into recycle, the pump should also continue to run whatever the anticycle time is.

 

[V1ks44]

How many rads?, have you tried it with both rads and UFH on together?, would also suggest increasing the flow temp to 65C and the anticycle time d.002 to 30mins, this gives a actual anticycle time of 6.5mins, if you do this then note that the actual time is 6.5 minutes when it goes into recycle, the pump should also continue to run whatever the anticycle time is.

I have 4 Rads and 2 Towel rails (in Bathrooms), let me try increasing the temp to 65c later on today, I have Hive TRV on all 4 rads so i will set the temp to say 20c and change the d.002 to 30min as you say and the test how this goes along with the ufh being on as well.

After the boiler has gone into anticycle mode should it stop completely for the brief moment as mentioned above? Would a video help, i can upload something and share it.

on a side note am i right in thinking that when running just the UFH say at 60c and the manifold TRV set to 45/50 - this setup is returning the water too hot back to the boiler hence it could be going into anti cycle mode or it doesn't matter what flow i set on the boiler this will always happen, or isit normal for the boiler to be in anticycle mode x many times during the running of UFH. At the moment im just confused as to what is a "normal" setup?

When i check d.41 - return temp on the boiler whilst the boiler is in the process of heating the water back to the desired flow temp (e.g. 60c) i find the return temp will start going from 54c to nearly 60c and the boiler will continue to overshoot to 65c and then when it stops at 65c (flow) then return would be at around 60c....then anti cycle kicks in and the flow starts to drop down along with the return...as you would expect >>>> is this expected behavior?