Vaillant Ecotec Plus 825 or 832

[Speshact]

I'm not a heating expert or indeed very good at technical stuff at all and would welcome some YACFers input! Thank you.

1. Boiler choice and size.
 Our plumber has recommended the 832 on the basis of two people wanting powerful hot showers at a time, but he hadn't really considered the lowest heat output ('cos people always ask for more whoosh). I will look at other boiler options but to keep this simple, can we please just keep this to 'is the 825 an adequate option instead of an 832?'

My question about the Ecotec Plus 32w is whether the lowest heat output of 5.5kW means that, for almost all of the winter, the boiler is less efficient  than if the lowest heat output was 3.8kW.
Might a 25kw (825, 3.8kW min heating output, 10.5LitresPerMinute hot water flow) be a better option for us, as outlined below, than the 32 kw (832 5.5kW min heating output, 13LPM)?

As I understand it our 3 storey end of terrace, 3 bed one bathroom plus en-suite shower room 1984 house is likely to have a maximum heat requirement of 7kW on a very cold day, as we have double glazing, cavity wall insulation and are about to be able to further improve our loft insulation to fabulous when the water tank goes. We are happy to heat the house in the 18-21 degree range.
I gather that the boiler thermostat should be at 65 degrees to get an effective convection return of 45 degrees, making sure to put it on in time to bring the radiators and hence rooms to the comfortable setting rather than turning up the thermostat for a quick blast.

While we want two showers operating from the boiler we don't need to have them working at a time (three people in the house, none needing to depart at the same time in the morning etc. and I tend to shower at the leisure centre. Not planning to move for at least five years), plus we have a cold input washing machine and dishwasher.
I'm assuming we'll have eco shower heads which reduce the water use by aerating it so it still feels reasonably strong, but less water needs to be heated.

I'm not sure what water flow is required at what temperature to have two showers running adequately at a time in this three storey house - Does the 832 allow two showers at a time (and does the 825 allow two feebler ones?). It seems that:
If we cater for both showers being used at the same time we require a 12-16 litre per minute hot water flow
If we cater for one shower being used at a time we require 9-12 litre per minute hot water flow

Vaillant Ecotec Plus 832, 5-10yr guarantee, Maximum DHW output kW 31.8, 13LPM
Nominal heat output range of CH at 50oC flow/30oC return kW 5.7 - 25.7
Nominal heat output range of CH at 80oC flow/60oC return kW 5.2 - 24.4

Vaillant Ecotec Plus 825, 5-10yr guarantee, Maximum DHW output kW 25.4, 10.5LPM
Nominal heat output range of CH at 50oC flow/30oC return kW 4.2 - 20.4
Nominal heat output range of CH at 80oC flow/60oC return kW 3.8 - 19.3

Bonus questions:
2. Central Heating Control system
Which one - the manufacturers (eg Vaillant vSMART) or a Nest OpenTherm or...?

3. Deaerator
Put one in? https://www.jtmplumbing.co.uk/water-treatment-filters-c435/spirotech-domestic-range-c356/spirotech-spirovent-rv2-air-separator-brass-p20387/s24002

[chrisbainbridge]

Having had a vaillant, I would never have another one.  They are rubbish.  We ended up on first name terms with the engineer, it was so bad.

After 3 years we replaced the boiler and fitted a Worcester bosch.  I would never fit anything else.

[grams]

10.5 litres/minute for one shower is a huge amount, especially if you’d be mixing it with cold.

Check your existing shower by sticking a jug under it for 6 seconds and multiplying by 10.

[Speshact]

10.5 litres/minute for one shower is a huge amount, especially if you’d be mixing it with cold.

Check your existing shower by sticking a jug under it for 6 seconds and multiplying by 10.

Brilliant suggestion. I've checked each of our existing electric showers (consecutively). We get 5 litres / minute currently!

[Mrs Pingu]

You might want 10L/min if you have one of these newfangled drench showers and want to be able to do the washing up or put the washing machine on at the same time though...

[Speshact]

You might want 10L/min if you have one of these newfangled drench showers and want to be able to do the washing up or put the washing machine on at the same time though...
[/quote
Pleasingly both the dishwasher and the washing machine run off cold mains so that's not an issue in this case, and fortunately we're quite content with the shower pressure we currently have.

I've Googled drench showers, though, and think we'll be okay without this type, C-19 developments depending! https://www.hughes-safety.com/indoor-emergency-safety-showers/drench-showers.html?gclid=EAIaIQobChMIxLK-ttqV6AIVh7PtCh1T1AD7EAAYAiAAEgKrY_D_BwE

[Polar Bear]

Having had a vaillant, I would never have another one.  They are rubbish.  We ended up on first name terms with the engineer, it was so bad.

After 3 years we replaced the boiler and fitted a Worcester bosch.  I would never fit anything else.

And yet ours has been totally reliable save for one diverter valve for 14 years.   Would definitely have another if this one somehow gets beyond repair though a heat pump will probably be the next thing.

[Canardly]

Vaillant here 14 years and counting.

[Gattopardo]

How long is the manufacturers guarantee for and what do you have to do to keep it.

Have you got a filter for the radiators and incoming water pipe have a softener fitted?

[Speshact]

How long is the manufacturers guarantee for and what do you have to do to keep it.

Have you got a filter for the radiators and incoming water pipe have a softener fitted?

With a 'Vaillant boilet protection kit'(magnetic and non-magnetic particle filter) there's an extended 10 year guarantee available on ecoTEC plus (up to 45kW) and ecoTEC exclusive boilers when installed and registered by a Vaillant Advance Installer. The boiler must be serviced annually by either a Vaillant engineer or a Gas Safe registered engineer.

We'll consider fitting a water softener in the next phase of works.

[Tim Hall]

Regarding your bonus Q2, I've just had a glow worm combi boiler fitted, which is controlled by their MiGo system. AKAIK Glow worm are made by Vaillant these days and vSmart and MiGo are the same under the badges.

My research suggested that Glow Worm boilers use a different protocol to that from Nest etc, so while you can use Nest, you get more control, specifically boiler modulation, by using MiGo, or in your case vSmart. The phone app shows how room temperature compares to demand temperature. It's a very flat curve, meaning the room temperature is where I want it.

[Quisling]

Q1:
the maximum efficiency will be when the boiler is in condensing mode when the return temperature to the boiler is around 55C or lower.  Efficiency is therefore affected by how well your boiler manages the flow temperature in order to maintain a return temp of <55C.
Boilers can do this either by switching on/off (cycling) or by modulating.  Modulating is limited by burner design and the effective "turndown ratio" is anywhere between 1:5 an 1:25.  Assuming 1:5 then the boiler can modulate the burner down to 20% of the maximum boiler OUTPUT capacity so if the capacity is 32 kW then the minumum output is 6.4kW but the boiler also then has the option of cycling on and off below that point as and when there is a call for heat (which will either be managed by a room thermostat or by a sensor noting return temperature from the heating circuit).
Broadly then, with modern controls either boiler should offer good efficiency and it's more important to ensure the return temperature is low enough to enable condensing than it is to worry about the size of the boiler.

Q2 - either will work.  Check what facility you have with either option to control your boiler remotely via an app, and whether or not you actually need this?  Will the new controls have weather compensation - i.e. monitors outside air temperature and then automatically reduces the flow temperature as the OAT rises?  I think this is pretty much standard for Part L of the building regs now.

Q3 - yes, if you don't have any de-aeration fitted already it's worth the extra few quid if you can afford it and is considered best practice.

[Tim Hall]

Q1:
the maximum efficiency will be when the boiler is in condensing mode when the return temperature to the boiler is around 55C or lower.  Efficiency is therefore affected by how well your boiler manages the flow temperature in order to maintain a return temp of <55C.
Boilers can do this either by switching on/off (cycling) or by modulating.  Modulating is limited by burner design and the effective "turndown ratio" is anywhere between 1:5 an 1:25.  Assuming 1:5 then the boiler can modulate the burner down to 20% of the maximum boiler OUTPUT capacity so if the capacity is 32 kW then the minumum output is 6.4kW but the boiler also then has the option of cycling on and off below that point as and when there is a call for heat (which will either be managed by a room thermostat or by a sensor noting return temperature from the heating circuit).
Broadly then, with modern controls either boiler should offer good efficiency and it's more important to ensure the return temperature is low enough to enable condensing than it is to worry about the size of the boiler.

Ooh, slight hijack if I may. When my boiler was fitted the plumber turned the flow temperature down to 55C, to ensure condensation happened.  When, a couple of weeks later, the MiGo controller was fitted the ability to tweak the boiler flow temp directly from the front panel of the boiler was no longer available. However it shows as 75C.  Presumably the modulating you mention still allows condensing to occur.  There is the ability to change the "heating curve" which changes the rate the room heats up and presumably the flow temperature.

Q2 - either will work.  Check what facility you have with either option to control your boiler remotely via an app, and whether or not you actually need this?  Will the new controls have weather compensation - i.e. monitors outside air temperature and then automatically reduces the flow temperature as the OAT rises?  I think this is pretty much standard for Part L of the building regs now.

MiGo/vSmart includes weather compensation, based on getting the temperature from web location.

[Speshact]

Thanks to everyone for their input. 832 for two showers at a time, plus the vSmart control won the day.