Boiler recommendations please?

[Harry Bloomfield]

I have decided my Ideal Icos HE18 is beyond sensible repair cost, I have chucked enough at it, so I am looking now for a replacement...

It needs to be a regular, vented system type boiler, but if possible with separate boiler output temperature controls when heating the hot water tank, to that when heating the radiators. Yes I presently have a room stat and a water tank stat. I just like the hot water to be able to be very hot 80C, I appreciate that is above the efficient condensing range, but to heat the radiators the boiler output temperature need not be quite so hot. 18+ Kw needed as present boiler is adequate. The predecessor to that was around 32Kw, but some good insulation has made that high an output unnecessary.

I had no input into the boiler make last time around, this time I am looking to Vailant or Worcester/Bosch for a more reliable boiler.

[newshound]

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.

[Bob Minchin]

Isn't Greenstar a WB model name?

[Tim Watts]

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:

1) Highest DHW output for a wall mounted unit; 2) Reasonable price; 3) Easy to wire and operated (either dumb knobs or LCD depending on model) 4) Quiet and well behaved; 5) According to my Gas Fitter, WB parts are quicker to get hold off than Viessmann, maybe because it's more common???? *Anecdotal*

Viessmann:

1) Weather compensation that WB don't have (unless you buy their fancy controller that precludes using your own controls) - you only need add the sensor to a north wall (or shaded area I assume);

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.

[Tim Watts]

Yes.

[newshound]

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

[Harry Bloomfield]

It happens that Tim Watts formulated :

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

[Tim Watts]

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.

[Tim Lamb]

:-) 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.

[Harry Bloomfield]

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?

[John Rumm]

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...

[John Rumm]

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.

[Harry Bloomfield]

John Rumm explained :

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

[Harry Bloomfield]

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..

[Dave Plowman (News)]

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

[ARW]

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

[Harry Bloomfield]

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.

[tabbypurr]

My Vaillant does that.

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

NT

[Harry Bloomfield]

[e-mail] 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.

[John Rumm]

The 400 used to... Looking at:

(2005%20-%202015)

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

However the current model has a radically different internal layout:

(2016%20-%20Present)

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).