help with ecoTEC valliant 831 and heating

[MW9]

Now that you have established the position of the return sensor, its more than likely that its reading correctly, strange that the circ pump stops though as it shouldnt during recycle conditions, next time you are doing a few tests check the S status parameters. Also the burner shouldnt cut out at its target temperature of 75C, it should rise to 80C but if the rate of rise is very rapid, easy to miss. I have read of several Vaillant owners where the burner is cutting out at only a few degrees above the target temp but this isnt your root problem.
If you assume the average boiler heat demand is say 8hw, just below its minimum output of 9kw, then assuming the rad returns at 33C and a 75C/70C boiler flow/return will mean that the circ pump flowrate is 22.93LPM of which 20.2LPM is recirculating and only 2.73LPM is circulating through the rads, normally one would expect ~ a dT of say 15C through the rads or a circ flow of 1.0LPM/kw of rad output so the rad circ rate should normally be at least 8LPM for that 8kw output.

thanks so far for the input, I have recorded 2 vids to show how the temp is rising

I have put links to one drive as they are too big the link will expire in few days should be enough to watch it

Error

mietek-my.sharepoint.com

what I notice when I set the flow temp lower to 60 the initial raise of the temp was more stable and the boiler didn't cut off quickly, but then the flow temp is set to 75 the raise was quick on pump set to auto and then it cut off at 80, drop the flow temp to 44 and then burner kick in again , I then changed the pump to 100% and it was raising up better. (the reason why I have flow temp higher is I have hot water tank and it feels warmer with struggling radiators in winter I'm sure once the issues are resolved it can be set lower)

I'm still not sure about this return temp d41 as its always 5 degree lower then flow temp, I have jump through d40 and d41 on the video to show, the sensor position explain why it shows higher reading and most likely it working correctly but I don't know why the return water is hot inside the boiler but is not coming back from radiators, is this the bypass and if yes what could be causing it and should it be behaving like this?

edit;

I have done another couple vids and one 7 min long to show that even with lower temp it will cut off it will just do it slower, with higher temp it just goes there faster and the speed of this happening is faster.

 

[Johntheo5]

The by pass is factory set at 2.5M and I presume is spring loaded and will just open more and more if the resistance to flow increases so if you shut the boiler flow then the pump would just recirculate all the water through the by pass but the temp would rise very rapidly as only the boiler contents of 2 or 3 litres is being heated. As I said earlier I've allways thought that a 2.5M setting is very low, the remaining head is still further reduced after passing through the boiler Hex, I have an oil fired boiler which has practically no pressure loss through its Hex because its just a steel box full of water but I still require a pump head of 3.6M to circulate ~ 12LPM through 12 rads. Your system though even if you doubled the head will only increase the flow theoretically by 40% which still only gives you 3.8LPM.

You have a HW cylinder as well, assuming the series 8 vaillant is a combi? , if you increase the cylinder stat to ensure a circulation through the coil and also have the CH on what is the dT then at the boiler?. or is it a stored combi?.

 

[MW9]

yes it is combi boiler ground sink is supplied directly thorough boiler and the top bathroom showers are using hot water tank and pumps

if I increase the stat on the tank and put both CH and hot water tank the difference between d40 and d41 is still 5 degrees and the flow temp still goes above the set temp and cut off.

and that one radiator is still cold, that radiator is on the zone 2 which is heating 1st floor and loft but that particular radiator in in the ground floor next to entry door so the flow pipe comes down from the first floor and the return pipe goes back up to first floor so not sure if this is related to the pump head ? the boiler is on the ground floor and the main pipe goes to the first floor through the extension roof and I think it splits there, only 2 radiators on the ground floor next to the boiler are supplier directly via pipes on the ground floor, the rest goes up and comes down.

if I run just hot water tank alone it behave exactly the same it use the heating flow temp, goes 5 degree above and cut off and the difference between d40 and d41 is just 5 degrees

 

[Johntheo5]

If you run the cylinder on its own does the coil return feel hot and does it feel hot under the boiler and what is the d40/d41 dT then?

Boiler could be 10M below the rads and the only increase in head required would be due to pipe line friction losses, the elevation has no effect as its a closed loop, but pipes going down and up can contain air so maybe a few automatic air vents are required.

 

[MW9]

If you run the cylinder on its own does the coil return feel hot and does it feel hot under the boiler and what is the d40/d41 dT then?

Boiler could be 10M below the rads and the only increase in head required would be due to pipe line friction losses, the elevation has no effect as its a closed loop, but pipes going down and up can contain air so maybe a few automatic air vents are required.

when only cylinder runs the return pipe does not feel hot under the boiler, I will check the return around the cylinder once it heat up again but if it's not hot under the boiler it wont be hot there either

for the automatic vents do you mean those ?

https://www.amazon.co.uk/Aladdin-Bleeding-Automatic-Radiator-Single/dp/B019395RHY/ref=sr_1_18?keywords=auto+bleed+radiator+valve&qid=1691615149&sr=8-18

I looked at them at some stage but I was worried that they might just randomly leak

 

[MW9]

ok when I run just cylinder the return pipe feels much warmer at the cylinder and under the boiler, probably not as hot as the d41 shows but its very warm I can hold it maybe 15-20 sec and gets very warm in the hands, where the flow I can hold it for maybe 2 sec before its burning my hand

where I run central heating then I can hold the return indefinitely at the boiler.

there is one designer rad above the one with issues downstairs which seems to have a little bit of air, it does not stop it to heat up but maybe its causing issues on the one downstairs ? if I empty the air today it will have a little bit again tomorrow.

 

[Johntheo5]

when only cylinder runs the return pipe does not feel hot under the boiler, I will check the return around the cylinder once it heat up again but if it's not hot under the boiler it wont be hot there either

for the automatic vents do you mean those ?

https://www.amazon.co.uk/Aladdin-Bleeding-Automatic-Radiator-Single/dp/B019395RHY/ref=sr_1_18?keywords=auto+bleed+radiator+valve&qid=1691615149&sr=8-18

I looked at them at some stage but I was worried that they might just randomly leak

No not that type, the ones that are teed into the piping, like the one below.

ok when I run just cylinder the return pipe feels much warmer at the cylinder and under the boiler, probably not as hot as the d41 shows but its very warm I can hold it maybe 15-20 sec and gets very warm in the hands, where the flow I can hold it for maybe 2 sec before its burning my hand

where I run central heating then I can hold the return indefinitely at the boiler.

there is one designer rad above the one with issues downstairs which seems to have a little bit of air, it does not stop it to heat up but maybe its causing issues on the one downstairs ? if I empty the air today it will have a little bit again tomorrow.

Did you note the d40/d41 dT, the cylinder coil except you have a balancing gate valve throttled in on the coil return should circulate very rapidly with a pump head of 2.5M so there should be little or no difference between the return pipe and d41 with little or no bypassing. Its possible, I suppose that the by pass is stuck open or malfunctioning, mention this to the engineer.

The designer rad is possibly just gathering air thats in the system as its high up but should eventually stop.

 

[MW9]

I might have one of those valve next to cylinder, the difference between d40 and d41 is about 4 degrees, the return pipe feels much warmer then when running radiators.

The boiler goes above the flow temp as well and cut off but it could be that the cylinder is already hot or maybe the same issue as in CH

 

[Johntheo5]

That just looks like a blank, you wouldny want to remoe that with a pressurized system but sonetime when next depressirized you could just have a manual lever valve ready to install after removing the blank.

Yes, I'd say with a hot cylinder that the coil won't absorb 9kw as you would need a unlikely flowrate of 32LPM at a dT of 4C

 

[DP]

OP, read up how to balance a system.
There are engineers With vast experience not posting because you are tinkering with setting etc that are base less.

If you could mark a slug of water moving through the pipes, as it meanders through the system, it needs to cool down by 20 degrees by time it returns to the boiler. Ie, leaves the boiler at 70, comes back to the boiler at 50.

You are closing the lock shield without reason. ALL the valves and zones need to be fully open and progressively restricted at the lockshield to achieve 20 degree drop. Does the HW zone got a lockshield? Do you have room thermostat to control the zone valves?

If you have been thorough like you mention, I would do couple more evacuations and refills. Check colour of water that comes out. Even using the method you employ will never remove all the water or debris, each continued fill and drain weakens what is left in the system.

 

[MW9]

OP, read up how to balance a system.
There are engineers With vast experience not posting because you are tinkering with setting etc that are base less.

If you could mark a slug of water moving through the pipes, as it meanders through the system, it needs to cool down by 20 degrees by time it returns to the boiler. Ie, leaves the boiler at 70, comes back to the boiler at 50.

You are closing the lock shield without reason. ALL the valves and zones need to be fully open and progressively restricted at the lockshield to achieve 20 degree drop. Does the HW zone got a lockshield? Do you have room thermostat to control the zone valves?

If you have been thorough like you mention, I would do couple more evacuations and refills. Check colour of water that comes out. Even using the method you employ will never remove all the water or debris, each continued fill and drain weakens what is left in the system.

As I said above I have read up many times on the balancing and I have tried to do it again yesterday, but when I open all the valves and lock shields not all radiators will get warm so I can’t even finish the first step of marking them in which order they heat up. The boiler will heat to set temp flow and will cut off waiting for the flow to cool down and restart again and it will go like this for hours and 2 hours later no more heat will progress in radiators, from 15 radiators I managed to get to nr 7 where 5,6 and 7 where just lukewarm half way through.

I will try to flush the system couple more times over weekend.

 

[Johntheo5]

IMO, the very first important thing is to get the boiler to fire continuously without cycling, even though this boiler has a relatively high minimum output of 9kw it should not be a problem, normally, with all the rad valves opened fully to achieve at least this, I have tipped around with a good few relations rads, including my own, for the past 50 years or so and with a clean system and a pump head of 3.5 to 4.0M this will result in a rad/boiler dT of ~ 9C to 12C with no balancing, its relatively easy then to balance but not a hope IMO to balance a system as above. It has been more or less proved that the flow through the above system is only ~ 3LPM!. Even 3 rads alone of any size should give this flow.

Even though a pain, it might be worth isolating the boiler, remove the flow and return, connect a mains hose to the flow pipe with a PRV capable of reducing to 0.5bar (5M) (1bar will do, if not) and run the water from the return into a container with various combinations of zone valves latched open, this will give you almost 100% accurate flow rates, can be corrected for the actual pump head.

 

[MW9]

So I have drain water from the magnetic filter and dirty water came out so I’m draining the system again and will do it few times this is the water is coming out from the hose not sure if it’s dirt or it’s colour from inhibitor I have uploaded the video to one drive as I can’t post videos here

I have bought x800 as well so after I flush it few times I will run this for a day or 2 and drain few times again before adding inhibitor just to make sure it cleans the system again

 

[MW9]

I have a bit of dirt from magnetic filter at the bottom and made picture as well if the water from the drain

 

[Johntheo5]

Are you flushing through the boiler as well as through the rads or are you just flushing via the flow/return with boiler isolated?.