Boiler recommendations please?

I've a Vaillant Greenstar of some sort, it has separate controls for hot water and radiators but TBH I'm not sure how it works. All the manuals are easy to download.

I have a simple W plan and IIRC the diverter is switched by the cylinder stat. Don't know if the boiler temperature is controlled at the same time with the default "simple" control system.

Boiler has been very reliable.

Isn't Greenstar a WB model name?

I heavily researched Viessman and Worcester Bosch:

I went with WB, but I would not be that unhappy with Viessmann either.

Pros and cons (WB substantiated, Viessmann is based off anecdotal evidence and on paper specs - at least one person here has a Viessmann and will probably comment)

WB:

Viessmann:

2) Slightly more "Waitrose" than WB's "Sainsbury" - stainless heat exchanger supposed to be a selling point.

I went WB mostly because it had enough DHW power in theory to run a shower and a bath (latter is throttled to 20l/min by flow restrictors).

I do miss not having weather comp, but I have measured the flow and return temps for each number on the knob - and have a rough manual scale of "this time of year, turn knob to 4" kinda thing.

Yes.

Oops yes I mean ecoTEC! But WB and Vaillant seem to rate equally highly both here and in Which?

It happens that Tim Watts formulated :

I don't want/need DHW, I like stored HW.

Well then - look at there non combi range - most of the Pros and cons are likely to be much the same. But you could easily look at the Viessmann with weather comp.

:-) I have just fired up a 30kW Viessmann in the cottage. I'm not yet familiar with the controls. Weather comp yes. Different temps. for hot water and heating, yes I think. You can certainly switch off the heating for summer. Clear display.

I have a 30kW condensing boiler and new flue for anyone offering an appreciative home. 5 years old (2 years work and 3 resting). Potterton precision.

Tim Lamb wrote on 24/03/2018 :

I cannot seem to see a name for the independent boiler output temperature limiting - anyone, what is it called?

Is it available on a regular, open vented boiler?

Vaillant 400 series do vented and split temperature operation. They can also do weather compensation if you want. Been very pleased with my 600 series system boiler so far...

Not quite sure what you mean? Or are you referring to "split temperature operation" - the ability to run the heating and hot water at different flow temperatures (or the heating under the control of a weather compensator, and the HW on fixed temp)

Split temp, yup see my other post. If Gremlin95 is about, he knows more about the new range than I do.

John Rumm explained :

Yes, that's it, 'split temperature' was the expression I was seeking. Thanks !

John Rumm laid this down on his screen :

Thanks, I will take a look at those. I just to be armed for when a guy comes around to give a quote..

You might find a maker won't warrant an open vent type these days. And many system boilers come with a pressure vessel installed.

Get BG in for a quote. Obviously do not uses them but have a holiday with the money saved!

Harry Bloomfield was thinking very hard :

Having enquired with both Worcester and Vaillant, neither offers a regular / conventional boiler which includes an ability to set two separate output temperatures for heating and hot water. A gap in the market me thinks, for an enterprising boiler manufacturer.

A single boiler setting stat is fine, where a consumer is happy with a lower temperature of boiler output for both heating and HW, but less useful for someone like me who likes their HW hot - where there is a possibility for some saving on keeping radiator temperatures lower, so the boiler remains in the more efficient condensing temperature range.

I suppose I could do an add-on stat, mounted on the flow pipe to the radiators, to shut the boiler down at say 60C leaving the boilers own stat set to maximum ? Would that not wreck the boiler's efficiency?

My current scheme is to manually tweak the room stat, gradually raising the room temperature to the desired temperature, over a couple of hours. Otherwise the heating system over reacts if the stat is set to desired in one single movement of the dial.

My Vaillant does that.

quite the opposite, it forces it to condense more of the time.

NT

snipped-for-privacy@gmail.com brought next idea :

Is that a conventional / open vented boiler, if so you need to let Vaillant know that they do actually produce one.

I am aware that it is often fitted to sytem and combi boilers.

The 400 used to... Looking at:

You can see that one has the two temperature controls on the front.

However the current model has a radically different internal layout:

But, a quick read of the manual still suggests that it supports separate CH and DHW temperature controls:

It also still has a connection for an external temperature sensor - suggesting it ought to work with the weather compensating controls. If that is true, then it must support split temp operation...

Yup:

Says that it works on all current models.

On mine (600 series system boiler) I let the weather compensator chose the CH flow temp (at installation you can select a variety of response curves that dictate how aggressively it ramps up the flow temperature in response to the external temperature falling). That tends to mean for the parts of the year where it not that cold out, it often runs flow temperatures in the 40 to 50 degree range.

The DHW I have set to 60 (its set at the boiler - there is no conventional cylinder stat - just a NTC thermister in a pocket that connects to the wiring centre). The boiler tends to run flow temperatures appropriate for that, usually doing the first bit of the recharge at around 60 to eek out more efficency, then ramping up to 75 ish for the last bit. I also have it set to do an anti-legionella cycle once per week - where it will heat the cylinder to 75 once. (its a hard water area, so lower cylinder temps result is less scale deposition).