Vaillant Eco Tec plus 837 Setup help

[hundleton1]

Hi guys, first thing i am an domestic appliance engineer and gas safe registered but don't do boilers, fires and cookers only, last year we moved into our first house that has had a new boiler a bout 3 years ago, its a 28kw eco tec plus 837, now its only a small house and i believe its was oversizes as the last owner had intensions to extend but moved instead

although the boiler runs happy im convinced its not 100% happy, after looking into everything iv found its massively over rated, based on calcs our house should need 15kw, based on the sizes of the 7 radiators fitted they come to a total of 29,000 but which calculates to 8.5kw.

obviously we are massively over rated, been in the boiler settings and d.0 was set to 28 so it was on max, i have no dropped it to 16, iv also extended the pump over run as 5 mins did not seem long enough.

i know this is a modulating boiler so should sort its self out to a point but frim the spec it stated at 60 degree its range is 12 - 28 on the central heating, is that the min and max modulation rate ?

Any suggestions on best settings to get the most out of this

thanks in advance [/b]

 

[D_Hailsham]

You have a 28kW boiler, but only need 15kW to heat the house. You also only have 8.5kW of rads. That sounds crazy.

How did you size the boiler? Did you use the Whole House Boiler Size Calculator?

How did you work out the rad outputs? Stelrad Elite Catalogue is useful.

Yes, 12kW is the minimum output and 28kW the maximum. If you only need 15kW, your boiler will spend most of its time switching on and off as it will only need more than 12kW when the outside temperature is below approx 3-4C.

 

[hundleton1]

Yep i sized the boiler from that chard and the calcs sheet you posted put me at 9.6kw a bit more that how i worked it out but im still well under.

im considering adding a vented cylinder to the CH feed and feeding the bath of that and leaving the rest of the house on the DHW as im replacing the bathroom this year, would give me a few more KW towards the boiler minimum

 

[hundleton1]

i am after some info on the modulation side of the boiler, from what i understand it recuses power whilst trying to maintain the target water temp and get the return temp down low enough to condense.

what conditions cause it to enter anti cycling mode? is it only when the stat stops calling for heat or can the burning shut down if the return it virtually the same as flow due to not being able to modulate low enough due to the small system?

im just trying to understand how it behaves so i can move foward

thanks in advance

 

[D_Hailsham]

Yep i sized the boiler from that chard and the calcs sheet you posted put me at 9.6kw

Let's get this straight.

The whole house calc says you need a 16kW boiler and the Stelrad catalogue says you only have 9.6kW of rads. If so, you really need more/larger rads.

I assume you got the rad data from page 31 - headed 50Δt. If so, the actual outputs may be lower; it all depends on the flow and return temperatures are you getting.

I'm considering adding a vented cylinder to the CH feed and feeding the bath of that and leaving the rest of the house on the DHW

Presumably the cylinder will be on an S or Y plan?

 

[D_Hailsham]

i am after some info on the modulation side of the boiler, from what i understand it recuses (reduces?) power whilst trying to maintain the target water temp and get the return temp down low enough to condense.

Yes, the boiler will modulate to maintain the require flow temperature. The return temperature depends on the flow rate and the amount of heat extracted from the water as it passes through the rads.

Your Vaillant boiler can also be configured to maintain a fixed return temperature; but this is only used for underfloor heating systems.

what conditions cause it to enter anti cycling mode? is it only when the stat stops calling for heat or can the burning shut down if the return it virtually the same as flow due to not being able to modulate low enough due to the small system?

Anti-cycling operates each time the burner is turned off. If the boiler can modulate so as to maintain the set flow temperature, anti-cycling should not occur. But if the boiler is at minimum modulation and the flow temperature rises above the set point, due to the return temperature rising, the boiler will go into on/off mode and the anti-cycling will kick in.

The anti-cycling time set in d.02 is just the maximum; the actual time depends on the flow temperature. There is a table in the Installation Manual.

 

[hundleton1]

i am after some info on the modulation side of the boiler, from what i understand it recuses (reduces?) power whilst trying to maintain the target water temp and get the return temp down low enough to condense.

Yes, the boiler will modulate to maintain the require flow temperature. The return temperature depends on the flow rate and the amount of heat extracted from the water as it passes through the rads.

Your Vaillant boiler can also be configured to maintain a fixed return temperature; but this is only used for underfloor heating systems.

what conditions cause it to enter anti cycling mode? is it only when the stat stops calling for heat or can the burning shut down if the return it virtually the same as flow due to not being able to modulate low enough due to the small system?

Anti-cycling operates each time the burner is turned off. If the boiler can modulate so as to maintain the set flow temperature, anti-cycling should not occur. But if the boiler is at minimum modulation and the flow temperature rises above the set point, due to the return temperature rising, the boiler will go into on/off mode and the anti-cycling will kick in.

The anti-cycling time set in d.02 is just the maximum; the actual time depends on the flow temperature. There is a table in the Installation Manual.

Thanks for the prompt replies. Ill double check the rad output values again later as I used the first page with sizes on, we do need more rads, some will be changing when rooms get done.

Thanks for the info on the boiler, that's grate, so from what I believe I'm understanding the boiler will try and modulate to keep the flow temp as its been set but as the system is small the return temps are coming back and climbing to wards the flow temp, as this happens the flow temp also increases and goes beyond the preset and then the boiler will shut the burner down.

Is there a preset level above the set flow temp that it will shut down on, eg 10% ect ?

This house has been bodged badly over the years lol.

Edit.

Another 2 questions

I understand that d.0 will limit the output, will this go below the 12kw modulating temperature or is that the lower limit?

And secondly if I understand correctly if i reduced the ch temp to a lower value the cycling would get worse as the temps would rise to quickly, I'm guessing It adjusts flow temp by lowering the burner and Increasing the flow rate ? If so I guess this also relies on the system being able to dump the correct amount of heat.

 

[Agile]

It pretty much turns off at the set flow temp.

It then enters an anticycling delay plus any longer until the flow temp falls until it fires up again.

If your house really needs 15 kW then you should add some more/larger rads!

Tony

 

[David937]

Two things trigger anti-cycling:

The burner will turn off and go into anti-cycling mode as soon as the flow temperature creeps up 5ºc above the set-point.

It will also go into anti-cycling if the room temperature is achieved and the room stat stops calling for heat to stop it firing again so soon if the room stat starts calling for heat once again.

 

[D_Hailsham]

I understand that d.0 will limit the output, will this go below the 12kw modulating temperature or is that the lower limit?

No; you cannot go below the 12kW lower limit.

if i reduced the ch temp to a lower value the cycling would get worse as the temps would rise to quickly, I'm guessing It adjusts flow temp by lowering the burner and Increasing the flow rate ? If so I guess this also relies on the system being able to dump the correct amount of heat.

If you have a lower flow temperature, the boiler will not need to run at such a high output. As you are already running at or below the minimum, it will go into anti-cycle mode more often.

Flow rate depends on pump speed and system resistance, which will vary as TRVs open/close. The pump has only two speeds, which are controlled by d.19. This means that the return temperature will depend on: flow temp; pump speed; heat extracted by the rads.

Don't forget that you only need 15kW when it is -1C outside. When it is 10C outside you will only need 7.5kW to heat the house (assuming 21C internal temp).

Tony and David937 are correct that the boiler will go into anti-cycle when the room stat turns the boiler off. I had overlooked that aspect.

 

[hundleton1]

thanks for all your responses guys iv got my head around it now,

performed some tests today,

basically if i set the target temp to 55, the boiler fires up and when i monitor d.40/41 flow and return temps, flow gets to 55, at this point the return is around 30, this then increases over the next 5 minutes,as it gets towards 47 the flow starts to creep above 55, when flow got to 57 it shut down, return was at 50 at this point.

a few hours later i performed the same tests again but with flow set at 70, was very much the same but over a far longer period, after 10 minutes, the return had hit 61, i shut it down at this point. all though this stops the short cycling it wont be condensing.

so one question is is it more economical to run at lower temps and short cycle it with lower d.2 times but it will condense or run it with higher temp with far less cycling but no condensing ?

another thing is it beneficial to lower the d.0 ? if its set to max does it run at full power until the target temp is achieved then modulate to maintain it or does it run at lowers possible whilst trying to increase to target ?

i have considered setting the pump to low speed but would this not cause the water to reach temp even quicker in the heat exchanger as its in there for longer ?


sorry to be asking more questions just want to try and make the best of a bad situation until i can try and make a more permanent solution

 

[D_Hailsham]

basically if i set the target temp to 55, the boiler fires up and when i monitor d.40/41 flow and return temps, flow gets to 55, at this point the return is around 30, this then increases over the next 5 minutes,as it gets towards 47 the flow starts to creep above 55, when flow got to 57 it shut down, return was at 50 at this point.

It sounds as if the boiler has modulated as low as it can, but is still supplying too much heat (Not surprising with 12kW going into 10kW rads), so it goes into anti-cycling mode.

What is the status (S) code when the boiler shuts down in this scenario?
How long before it restarts? (It should have been about 8 minutes with d2 set to 20 mins.)

a few hours later i performed the same tests again but with flow set at 70, was very much the same but over a far longer period, after 10 minutes, the return had hit 61, i shut it down at this point. all though this stops the short cycling it wont be condensing.

A pity you didn't let it run until it started to cycle.

so one question is is it more economical to run at lower temps and short cycle it with lower d.2 times but it will condense or run it with higher temp with far less cycling but no condensing?

You will have to experiment.

another thing is it beneficial to lower the d.0 ? if its set to max does it run at full power until the target temp is achieved then modulate to maintain it or does it run at lowers possible whilst trying to increase to target?

Anecdotal evidence from similar cases on this forum says that it is better to limit the max output using d.0.

i have considered setting the pump to low speed but would this not cause the water to reach temp even quicker in the heat exchanger as its in there for longer?

But the flow rate through the radiators is slower, so there is longer for the heat to be dissipated, which leads to a lower return temperature. The two things cancel each other out!

What is the d.19 setting?

 

[hundleton1]

Not noticed the S code will look tonight, is d2 not in minutes on the settings on the boiler ?, d19 is at default but im gonig to change to 1 tonight and try again ,im also going to drop d0 to minimum and see.


the good thing is the system heats up very quickly and the house can reach temp in no time, if i can just get it settled a bit better i will be happy until i can add larger rads.

was considering changing and adding a HW cylinder but i just dont think its worth the money

 

[scoobydo123]

or go for a stat with tpi logic. This wil monitor the required temp rise and turn the boiler on off and keep return low. First burn will have high return then it will do short bursts. Not sure on vaillant if this will trigger the anti cycle as flow target will not have been met. I have had good success with these type of controls on other boilers against weather compensation (outlay for WC is hard to justify as it takes a long time to recoup). Anti cycle is a matrix table that takes into account flow temp as an example if flow is 75 and d.0 is 60 then you will only get 2mins anti cycle. It is more designed around when you have WC so if a target flow of 40 is requested anti cycle will be much longer but it also starts counting and adjusts as temp drops. Maybe one of the vaillant experts will be along to confirm if anti cycle cuts in even if target flow is not met but you can always adjust d.2 down to min so as not to mess with logic of tpi stat

 

[D_Hailsham]

Not noticed the S code will look tonight, is d2 not in minutes on the settings on the boiler ?, d19 is at default but im going to change to 1 tonight and try again ,im also going to drop d0 to minimum and see.

You have to call up the Status Code via the Menu.

d2 is a strange beast! The setting shown in the display is the delay when the flow temperature is 20C. The delay then automatically reduces as the required flow temperature increases. If you don't have the installation manual, you will find a table showing how d2 changes here; see page 54.

d.67 shows how much time is remaining.

If you drop d.0 to minimum the boiler can no longer modulate, so it becomes a fixed output boiler.

If d.19 is currently on 2 the pump will already be running at the lower (1) speed for heating as you have d.0 set low; so you should not see any difference when you change d.19 to 1.