Vaillant ecotec plus 831 boiler broblem

[stevecase51]

A couple of months ago I had a Vaillant ecotec plus 831 combo boiler installed with a Vaillant VRT 350f programmable wireless room thermostat. Everything seemed to work OK on installation. The hot water works really well without any problems. With the rather colder weather recently, I have started to use the heating properly for the first time. When the room stat asks for heat, the boiler appears to go through the following sequence: (1) pump starts (2) burner fires and shows maximum on the left hand graphical display for a second or two, but then (3) drops to a low value and stays there. The flow temperature creeps up very slowly to the target value which I set to 65 degrees. Because the burner stays low, the radiators take ages to get up to 65 degrees. I should also mention that I have set the desired temperature on the controller several degrees above the room temperature to make sure this isn't having an influence.

I would have expected the burner to remain on full (or at a reasonably high level) and only modulate when the flow temperature approaches the target value. Installer can't come out for a few days. I would be very grateful if anybody with experience of this boiler/controller combination can suggest what the problem might be.

 

[DirksPlumbing]

Hi Steve, can you explain, why you need 65 degree flow temperature at this time of the year?

 

[DirksPlumbing]

Ideally a boiler keeps an as low temperature as possible. Unfortunately I do not know about your boiler/ room thermostat but I remember from ages ago that the Vaillant room thermostats did notify the boiler if the room temperature is close to target temperature to modulate down. This was done to prevent overshooting.

 

[justalex81]

define ages? sounds like its doing exactly what it should be doing to be honest. How the boiler fires is also determined by the difference between the flow and return temperatures and also whether or not you have weather compensation installed.

 

[stevecase51]

Thanks for your replies so far. To answer some of the questions you raised:-

By ages I mean more than half an hour. I was under the impression that modern boilers are supposed to get the house warm quickly, and then modulate the burner so that the system delivers just enough heat to keep the room temperature at the value set by the thermostat. Your reply implies that this is wrong, and the boiler is actually designed to heat the radiators up more slowly. Why would be the purpose in that? Or have I misunderstood something?

Why would I need a target flow temperature of 65 at this time of year? I don't know what it should be to be honest - the installer left it on the factory default value of 75 degrees which seemed a bit severe to me, so I reduced it to 65. I don't actually need any heat on right now, but I wanted to give the heating system a good run so that I can be confident it will do the business when I really need it.

I did wonder myself if the programmable thermostat is intelligent enough to tell the boiler the room temperature is close to the desired value (I haven't found anything in either the boiler or thermostat manuals to prove or disprove this). That's why I set the desired room temperature about 4 degrees above the actual for the purposes of my test.

As far as I know he VRT 350f does not have a weather compensation feature.

It would be really useful if Vaillant could spell out exactly what's supposed to happen so I can tell if it's behaving normally or not.

Steve

 

[Chalked]

Bet there's no permanent live.

 

[Rabbitman]

It could be a number of things, poor circulation through the system ntc's not reading correct temperature differential appliance sat in S53/54, the VRT not correctly set up or the most likely is D00 set to auto........... My money is on the latter

 

[dancinplumba]

Bet there's no permanent live.

its a combi

 

[stevecase51]

It could be a number of things, poor circulation through the system ntc's not reading correct temperature differential appliance sat in S53/54, the VRT not correctly set up or the most likely is D00 set to auto........... My money is on the latter

Sorry to seem so slow, but could you explain what the DOO is, how I can tell if it's on auto, and what it should be set to if not auto If this is the same thing as Code D.000 (Partial heating load) the manual (P52) says "a setting is no longer normally required".

 

[Chalked]

its a combi

I must read the full post. I must read the full post!

 

[Rabbitman]

This is probably where i get my hands slapped but D00 is the KW output of the appliance, the newer Ecotec comes factory set in auto (something they developed from the old glow worm adaptive control) and basically means the boiler is trying to select the kW output it thinks you require therefore certain days it can take longer to achieve set temperature than others........

 

[walterwhite]

Firstly, I would return the flow to 75 as your installer set it at that.....

 

[Rabbitman]

Firstly, I would return the flow to 75 as your installer set it at that.....

Ha ha i missed that, as above if your using the vaillant ebus controls always have the heating set to max.......... But id still have a peak at D00 lol

 

[walterwhite]

Yeah but leave D00 to the installer not the customer. ....

 

[Rabbitman]

I said i would get my hands slapped, so OP as Walter said go back to the installer should he know the answer............. I'm off back to Facebook lol

 

[stevetheplumber]

actually fault codes and settings that dont require the removal of the case might not be covered im not sure how would you feel if you were told you wasnt allowed to enter the computer on your car to check readings?

 

[walterwhite]

If I've commissioned a boiler & a customer goes in to the 'installer menu' sometime later, changes some settings, then calls me because it's not doing what it was...and then doesn't want to pay me for my time, I'd be a tad annoyed.

 

[AWheating]

Typical vaillent controls by the sounds of it, over complicated nonsense.

 

[DirksPlumbing]

I must read the full post. I must read the full post!

Hey, don't worry even on a combi a missing permanent live causes problematic behaviour of the appliance.

 

[dancinplumba]

Hey, don't worry even on a combi a missing permanent live causes problematic behaviour of the appliance.

yep, it wont work hahaha

 

[DirksPlumbing]

yep, it wont work hahaha

That could indeed happen. :lol: Though a permanent live is no guaranty. I had a spark wiring one permanently. I just had it on a plug temporarily. He rang me because the boiler would not do anything. He certainly had a permanent live in it ... and another one.

So you see, you still need a neutral too. I explained that to him and I think he got it. :artist:

:49:

 

[buckley plumb]

Fitted a few glowworm boilers and they seem the same when fitted with the climapro2 as they have room compensation..especially if the target temp is set bellow 70. Turn your room stat to full 30 and if this works you know it's the stat compensating.

 

[wattsie1987]

100% đ.00 phone your Installer to adjust.

 

[Stanios]

Had same issue with vaillant combi the boiler had this problem which persisted after vaillant checked it out (they fixed issue with flue noise but didnt bother to fix central heating). Bleeding the rads fixed it, there was an airlock somewhere, boiler modulates down due to restricted circulation.

 

[thomas donovan]

flow or return isolator underneath not opened so boiler just heating and flowing around the bypass, in this event the hot water will always be fine heating will play up.
I would give the engineer a call rather than tinkering yourself

 

[Stanios]

flow or return isolator underneath not opened so boiler just heating and flowing around the bypass, in this event the hot water will always be fine heating will play up.
I would give the engineer a call rather than tinkering yourself

yep or a shut off valve on a magnaclean is another common one

 

[stevecase51]

Waiting for installation engineer, but he says it will probably need visit from Vaillant.

Starting from cold the burner stays very low. If I turn hot water on briefly and then off again, this sometimes seems to kick the heating into life - the burner switches to a much higher power, and the radiators get up to temperature quickly as they are supposed to. Burner then modulates to maintain flow at target value.

Somebody else on adifferent forum has exactly same problem (but don't kow if they ever solved it)

Vaillant ecoTec plus 837 issue: Radiators slow to heat up | DIYnot Forums

 

[newcastle phill]

Anyone messed with the internal bypass. They are settable by an engineer.

Probably nothing to do with it but has it been checked and not backed right off or faulty

 

[stevecase51]

Anyone messed with the internal bypass. They are settable by an engineer.

Probably nothing to do with it but has it been checked and not backed right off or faulty

Actually I was wondering about the by-pass myself. Although I can't be sure yet I get the impression that on the few occasions when the burner has powered up properly without any intervention, all TRV's were fully open. Normally one is fully closed (unused bedroom) and another may be partially closed. I will mention this to the installer when he comes.

 

[stevecase51]

Installer called this morning and agreed this behaviour is not normal. He contacted Vaillant who are coming to look at it on Tuesday. Just out of interest, I'd be interested in knowing from those of you who install a lot of combi boilers: what is the tyipcal time taken to heat up the radiators (from cold to 70 degrees say) for a modern combi.

 

[newcastle phill]

Well many radiators never get to 70 degrees these days by designed giving a lower temp over a larger radiator surface area - its more efficient that way.

 

[stevecase51]

Nobody has suggested this yet, but could my slow warm-up problem be caused by the radiators not beiing balanced with a sufficient temperature drop, so the flow/return differential at the boiler is only a few degrees? Could this cause the boiler to restrict the burner?

 

[Rabbitman]

Nobody has suggested this yet, but could my slow warm-up problem be caused by the radiators not beiing balanced with a sufficient temperature drop, so the flow/return differential at the boiler is only a few degrees? Could this cause the boiler to restrict the burner?

Hi see my post no 7 poor circulation through the system could be a reason the radiators heat up slowly as the ntc's need to see the correct delta T, confirmed in d codes with the appliance sat in s53/54............ But as said get the installer back to look as this type of fault is usually confirmed using the 4 button display

 

[stevecase51]

It could be a number of things, poor circulation through the system ntc's not reading correct temperature differential appliance sat in S53/54, the VRT not correctly set up or the most likely is D00 set to auto........... My money is on the latter

Well it turns out you made the right call.Vaillant engineer called today. (Incidentally I was impressed with Vaillant who texted me to remind me he was coming, and then he phoned me early this morning to say what time he would arrive) Anyway he changed D00 from "auto" to 15 kW. He said that in 80% of intallations the heating output needs to be manually set because "auto" (which is a relatively new feature) doesn't work too well. He also found that the internal bypass valve was set to near the minimum pressure, which may not have been helping, and so he set it higher. Hopefully I can now look forward to shorter warm-up times when the cold weather sets in.

 

[rucky75]

Hi just been reading through your post, did the vaillant engineer solve your problem with his auto to 15kw change, were your radiators heating up quicker. I'm having a similar problem with a newly installed ecotec plus 832. Will call the installer but would be great on an update. thankyou

 

[gmartine]

Hi just been reading through your post, did the vaillant engineer solve your problem with his auto to 15kw change, were your radiators heating up quicker. I'm having a similar problem with a newly installed ecotec plus 832. Will call the installer but would be great on an update. thankyou

You may get a response but the thread is a year old, chances are it's okay or he would've reposted.

 

[stevecase51]

Hi just been reading through your post, did the vaillant engineer solve your problem with his auto to 15kw change, were your radiators heating up quicker. I'm having a similar problem with a newly installed ecotec plus 832. Will call the installer but would be great on an update. thankyou

Yes he did Heating has worked well - hope you get yours sorted

 

[rucky75]

Yes It did get sorted The engineer said the "auto" output setting often does not work well but seting D0 to 15kW was the answer

Thankyou for your reply, we are having exactly the same issue, heating taking 1/2 or more to get to the flow rate temp. Hot water fine, Installer is coming round next week, will mention your solution and take it from there. Again thanks

 

[ccarmock]

I have the same problem with an Ecotec plus 831 - . Was the fix setting D0 to 15 kW only or did you need more doing?

 

[rucky75]

I have the same problem with an Ecotec plus 831 - . Was the fix setting D0 to 15 kW only or did you need more doing?

Hi i lowered the DO down to 15, did'nt do anything else. Seem to solve problem. Scott

 

[MatthewHurt]

The VRT350F is a compensating control that will modulate the burner to achieve maximum efficiency during central heating operation. That does not mean that it will run full pelt, it may well run at minimum for an hour and should allow a very gradual heat up of the home, rather than running as a 'dum switch' which is either on 100% or off.
Adjusting the max heat load down to a fixed number just means that you've hindered the boilers ability to modulate and have effectively disconnected the main feature of your thermostat.
The D0 being set to auto is also a compensating feature, it means that you are able to use an old fashioned on/off thermostat, but set the boiler to modulate according to system demand.
It would be far more sensible to leave the boiler stat to do what it's built to do, and is often much cheaper to allow the boiler an extra hour or two to heat the house up by running at a very low rate, but if you're finding it takes far too long to heat the house then rather than setting D0 to a fixed number, you should adjust the heat curve of the controller (if a compensating control is fitted) to increase the boiler flow temperatures in relation to the given room temperature.