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!