Vaillant Total System Solution - inconsistent heating

To be honest, 37kW struck me as being rather large for 10 rads too.. Of course, they could be large rads in a large house
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I suggest you go to the boiler and press the i and + buttons simultaneously d 0 will be displayed. press the i button and 37 will be displayed, using the - button lower this figure to 25 and then press and hold i until display stops flashing.
The water heating system works fine; however, the central heating system doesn't.

So the boiler doesn't cycle on the Hot water but does on the CH. The water gets hot but the radiators don't.

This is a classic weather compensation set up problem.

Lowering the maximum output of the boiler will not increase the radiator temperature. Ecotec 637 will modulate down to 10Kw if it decides the load is not significant - whether or not you range rate it.

If there were not enough emitters the boiler would quickly modulate itself. Lowering the maximum output to 25Kw will not stop the boiler's own electronics from taking it down to 10Kw when it deems necessary.

The range rating scenario will save a small amount of energy in an ecoTEC by preventing the boiler from fully opening up at start up, but is much more relevant to non-modulating boilers. I do not think it has much to do with this problem.
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Heating Curve is set to the default factory setting of 1.2 degrees celsius.

How do I override the weather compensation and modulation settings? I would much rather prefer a situation where I can control how hot it gets and then manually switch it off when as I feel like.

House is larger than average with high ceilings and 5 bedrooms. In total, 7 radiators downstairs (2 of which are small) and 6 radiators upstairs (2 of which are small).

As a side issue, the VRC430 is now showing an extremely dim display. I've set the contrast to a maximum of 15 with no effect -anyone seen this issue? Also done a factory reset on it too. I've seen the display completely vanish at times also before lighting up blue again.

I'm scheduling for a Vaillant certified person to inspect the whole system at somepoint over the next week and will keep all updated. Thoughts and suggestions all welcome in the meantime.
That is your problem, as I pointed out some time ago......

It needs to be set in the region of 2.6 for a typical UK house. I suggest this will immediately fix your problem.

It is not degrees, it is the ratio between the outside air temperature and the internal water flow temp through the radiators. If you look in your manual you will see the graph showing the different response curves.

Remember to leave both the HW and CH knobs on the boiler fully clockwise, too.
I will try setting the heat curve to 2.6; however, is it really required to turn bith CH and HW dials to 100% ?

I'm happy with 55*C HW.
Apart from setting the curve correctly, I would still recommend setting the power output of the boiler to about 22 kW.

I think you have a massively over rated boiler. I really dont know why people so this.

The effect is that the boiler for most of the year cannot modulate down to the heat actually needed when its less than the boiler's minimum of 10 kW. It then has to cycle on/off which is less efficient.

Were the installers CORGI registered and have they notified CORGI who will send you a blue Certificate?

For now, I'm trying the following:

* Heat Curve set to 2.6 * C
* HW set to 55 * C
* CH set to 55 * C

I don't want to going beyong the 12 o' clock mark on the dials so to avoid build up of limescale etc. 55 * C water is hot enough.

Yes, I have received the blue CORGI certificate.

Vaillant is arriving onsite later this week (hopfully).
The max CH temperature should be set to at least 70°C.

However its the maximum boiler power that I think you should be limiting to about 22 kW.

I suspect the boiler is producing whatever flow temperature the w/c is asking it to but then it modulates down to minimum but is still unable to maintain 70° C with the minimum power output.

I also wonder if the system is properly balanced? Thats even more important than usual when your boiler is over rated. Just one rad on full flow will cause the return to rise so high that the boiler will turn off using the situation I have mentioned in the above paragraph.

Ideally the flow rate through each rad should cause the return of each rad to be about 20° C below the flow!

Excellent, looks like we're making progress here.

I've set the following and so far after 3 hours of the heating switched on, the on/off cycling hasn't occurred once:

- 52*C HW
- 55*C CH
- 3.0*C Heating Curve
- 37kW Boiler Rating

However, despite the continuous heating, the bottom part of the radiators still don't get as hot as the top. Will be testing the following setup over the next few days:

- 52*C HW
- 70*C CH
- 2.6*C Heating Curve
- 22kW Boiler Rating

Ideally, I would like to keep the temperature dials to less than 55*C so to avoid build up of limescale. Not too keen on water softeners yet.
Agile wrote

but then it modulates down to minimum but is still unable to maintain 70° C with the minimum power output.

If the boiler was trying to maintain 70c then why would it modulate down to minimum output ?.
Turn the heating stat on the boiler to full, but leave the HW sat at whatever temperature you want the water to be is one way, the other is to set the HW stat to max then set the DHW temp in the WC to 60C.
Ideally, I would like to keep the temperature dials to less than 55*C so to avoid build up of limescale. Not too keen on water softeners yet.

You seem to be under some kind of misapprehension here.

Its only the water temperature you need to keep below 60° C. That is to avoid scalding primarily as you still dont get lime scale deposition until a few degrees hotter.

Its not relevant on CH and in any case London water is not very hard anyway.

The manufacturer instructions say the dials should be set to 100% when under the control of VRC430.

Once again, the range rating of the boiler is not going to make any difference to the lowest modulation level, it is still 10Kw. By range limiting it you will only cut off the top end, not the bottom.

The boiler temp should be set to max to let the weather comp have total control.

You should stop fiddling now and follow the manufacturer instructions. Having silly ideas about limescale and turning everything down to what 'you' think is not going to work properly.

Once the weather response curve is set up you should allow the boiler logic to control the system, or you might have well not have bothered in investing in VRC430 in the first place.

The bottom of radiators does not get as hot as the top. This is a known factor with all radiators.

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