Vaillant EcoTec Plus 826 - is it too small and what controls to use?

[WakingDan]

Evening all,

I'm looking to have my 50 year old conventional boiler replaced with a combi, and may have a HWC added in a new location at a much later date.

The current boiler is a Potterton Netaheat Electric 16/22. The teeth on the knob on the front have gone so the actual setting is somewhere between 16kw and 22kw, and that does this house of 13 radiators (soon to be 12 and one isn't used over Xmas due to the tree) just fine.

The 826 used 19.8kw for heating and 26kw for the DHW. It can raise the water temperature by 30 degrees for a flow rate of 12.4 l/min or by 35 degrees for 10.6 l/min.

We have one bathroom with an electric shower over the tub, but wish to have a bath and separate shower cubicle in the same bathroom.

One installer believes the 826 is far too small and suggests going for 32 at least, preferably 36 or 40kw models.

Cost isn't the issue for me, just efficiency. The 26kw model modulates to 2.5kw, the 32kw down to 3.5, the 36kw down to 3.7 and the 40kw down to 4.5kw.

What do you guys think? Its a 4 bed detatched.

On the subject of efficiency, I am happy to go all in with weather comp but I have had mixed suggestions of vSmart, to staying away from Vaillant controls completely in favour of Hive, or for going going vaillant but ditching the weather comp and going for the room stat which uses load compensation.

What has been your collective experiences? The Vaillant website seems rubbish for making an educated guess as they market all of their products as being great.

Thanks all, Dan!

 

[cross thread]

How’s the cold water pressure / flow .as most combi boilers are a sealed system will your rads pipe work be ok

 

[WakingDan]

How’s the cold water pressure / flow .as most combi boilers are a sealed system will your rads pipe work be ok

The house was built in 1970 during the copper shortage and has a lot of truwell(?) pipework, however, I hung 11 new radiators and had the pipework fully replaced. The bathroom and kitchen radiators were lefts with the kitchen being pipes in copper and the bathroom being truwell.

The bathroom rad will be capped off for this reason, and the Mrs wants and electric one in there anyway.

I have checked the electric shower we currently have and it puts out 38 degrees at 6ltrs a minute at the setting used last by my wife. The mains pressure is very good here to the point I'll need to bring in a bucket from outside to do a proper flow test, however the current mains temp was 12.5 degrees.

 

[WakingDan]

Our kitchen tap appears to be giving out 24 l/min using a stopwatch and a 2.2 liter bottle of milk.

 

[cross thread]

Even the small combi will be enough output to heating , so if your happy with10 litres water flow why go bigger ,spend the money on a decent controls,thermostatic rad valves.

 

[WakingDan]

Even the small combi will be enough output to heating , so if your happy with10 litres water flow why go bigger ,spend the money on a decent controls,thermostatic rad valves.

Thanks cross

We don't know what a good flow rate is so when we stay somewhere with a shower we like we will have to perform a flow test and whack out the meat thermometer to test the temperature too I think

If we were able to get water into the house at 0 degrees, the boiler should put out 35 degrees at 10l/min Somebody running a tap for the kitchen sink or to wash their hands I guess might be an issue unless flow restrictors were installed? I have no idea what the lowest temp we are likely to get in the depth of winter, however, would it be an issue right now? To get 12 degrees upto 38 is 26 degrees, or 75% of its heating capacity at 10l/min