Attempting to balance rads with condensing (Vaillant) boiler

[diyn24318]

Hi all,

Apologies if I sound like a div writing this but, having followed the FAQ from this site, and read several times a couple of other articles on balancing, I am a bit stumped as to how to progress.

Q's:
Question 1 is regarding a condensing boiler not holding a constant CH temp during balancing.
Question 2 is regarding the drop required (I have it in my head 12C but read an article suggesting that condensing boilers need to be 20C - or is it just the diff between boiler flow and return temps?)

Scenario:
I have a detached 60's house with 5 rads downstairs and 4 upstairs. Boiler is a Vaillant ecoplus 428 with output set at 80C. Using a TPI 343 diff thermometer (as recommended in other posts on this site) to measure drop across the rads, but cannot get a temp diff that holds/is reliable/repeatable. Seems the diff is constantly changing, whether boiler is firing or "modulating"/cycling (?).

Questions:
Q1: Seems to me, to do the rad balancing, I need to have the boiler push 80C CH around until the thermostat says to stop (which, when balancing, will never do) - does that sound right?

If so, any ideas how to get my boiler to do that (i.e. just keep CH at same temp)?


Q2: what is the ideal drop for my boiler?


Any help very much appreciated - I'm struggling big time...


NB

 

[Agile]

I think that you need to read the FAQs rather better.

They may not be perfect but are not that bad!

Tony

 

[diyn24318]

I think that you need to read the FAQs rather better.

They may not be perfect but are not that bad!

Tony

Tony, I have read and re-read it several times but can't figure it out. The problem I have is, the diff is constantly changing (without me changing the LS valve).

Could you highlight where I need to read them better please?

 

[gazdaz36]

What is your main problem and why are you trying to balance the system. From the limited info you've given I would suggest that your boiler is too powerful for your system and causing problems heating the house up. When your heating is on try pressing the i button and see if a s53 status code comes up on the display

 

[St0rmer66]

Start by opening every rad only 1/4 turn open on the lockshield (do them ALL before you even touch a thermometer). It's a better starting point. Run the heating for a while until all rads are hot then start measuring. Make very small adjustments, leave it a few minutes, then measure again. It won't change instantly and you'll never get a perfect 20 degrees for 100% of the time (especially not with an over-sized boiler like you have). Smaller rad's especially it's a struggle to get 20 degrees.

 

[Agile]

If you must try to balance it then it helps to so this with system not too hot, flow set to 75 and d0 set very low so the boiler is not constantly cycling!

Tony

 

[diyn24318]

What is your main problem and why are you trying to balance the system.

The main problem *was* the boiler cutting out, however your next suggestion, and Agile's post, helped me to get past that.

From the limited info you've given I would suggest that your boiler is too powerful for your system

I have read this before and will look to reduce the power accordingly in the near future.

...and causing problems heating the house up.

House doesn't have a big problem heating up as such, though the back room is larger and does take a while to heat up due to placement of the rads - I have replaced the vertical designer rads I inherited on purchase last year with some Kudox double/double's, but need another on the outside wall facing into the centre of the room.

When your heating is on try pressing the i button and see if a s53 status code comes up on the display

I don't suffer from this problem though I have read that other Vaillant users do.

 

[diyn24318]

Start by opening every rad only 1/4 turn open on the lockshield (do them ALL before you even touch a thermometer). It's a better starting point. Run the heating for a while until all rads are hot then start measuring. Make very small adjustments, leave it a few minutes, then measure again.

I took your advice (thank you) and did this today. Two of the rads didn't get hot at the lockshield valve so I had to up the flow.

I believe I am making progress, however unfortunately I took so long the boiler reached the point it turned off regardless of the power output/temperature! I'll go again tomorrow.

However, this is sound advice and should be incorporated into the FAQ as I can't recall it mentioning letting the rads get hot on the flow and return valves/pipes *before* starting to take their temperatures.

It won't change instantly and you'll never get a perfect 20 degrees for 100% of the time (especially not with an over-sized boiler like you have). Smaller rad's especially it's a struggle to get 20 degrees.

So, to answer my Q2, I want a 20C drop across the rads and not 12C?

 

[diyn24318]

If you must try to balance it then it helps to so this with system not too hot, flow set to 75 and d0 set very low so the boiler is not constantly cycling!

So I set flow to 75

I set d0 to 8 - rad 1 seemed to struggle getting to sufficient temperature.
Set d0 to 12 and that seemed to work well (I vaguely remember reading these as agreeable values, though as I said earlier I will work out a correct output value for my rads and adjust d0 accordingly soon).

This was a big help BTW Tony, it allowed me to get 90% through the balancing - many thanks for writing.

 

[Agile]

Setting the d0 low while balancing reduces boiler output and ensures there is no chance of the boiler cycling off while you are doing the balancing.

Its not usually realised how helpful doing this can be.

70% of boilers are left with the manufacturer's default setting by lazy installers. Its easy to reset to the heat output of the rads plus 2 kW where a cylinder is also heated.

Also when balancing, the reheating of the cylinder needs to be turned off.

80% of cylinders dont have a lockshield to enable the heating and water flow rates to be balanced against each other.

Tony

 

[diyn24318]

I started the second part of the balancing this morning and have managed to get all the rads but two to have around a 12C drop. The two exceptions were both with a difference of 16C+ at the start and despite ending up opening the valves fully (expecting them to be the end of the run), they still have a 18C or so diff.

(Edit: Reading a few other posts reminded me my plumber said I had a diverter/bypass in the system - at present, it's not possible to adjust it as it has a pump in front of the adjustment screw! Could this be causing part of the problem?)

The two get fairly hot at the inlet (~55C compared with 60odd upstairs) but are cool at the return. Both are downstairs at the front of the house, and I believe one is run from the other (a new Kudox double/double 1200mm is run off a single fin 1200mm).

The three other rads downstairs, a 450mm wide single fin also at the front and two 600mm double/doubles (the new Kudox ones) at the back, are fairly spot on now.


My assumptions are:
- as the single fin is getting heat to it, and as it's a fairly large rad, heat is leaving the boiler quicker than the flow can be pushed through - OR there is a blockage/air in there
- the one run off it is suffering as a result
OR
- I need to reduce the differences upstairs so there is enough flow to push to the downstairs


Can anyone offer any pearls of wisdom please?