Ideal logic system boiler - PDHW

[Ben Blaukopf]

Just for information, because

a) It wasn't totally obvious that this would work b) The manual is extremely light on details c) There is no info I could find on the web about the V4043B wiring.

Had an Ideal Logic System 24 Max boiler installed.

I set it up as a PDHW system. There are two schematics on the web - one for the Logic Heat -

- and one for the Vogue - The only hint from the manual that it supports PDHW is the wiring diagram which has a separate CH and DHW live. My plumber was not confident that the Logic System would support what I wanted to do, so I rang up Ideal to check that if I connect to both DHW live and CH live I would get separate flow temperatures. They seemed to understand the question.

I wired it up as x-plan -

SL1 r CH and SL2 for DHW. I used a V4043B NO valve as shown on the diagram.

The NO valve has three wires. Blue/Brown/Green and is light on documentation, but wire blue to N, green to E, and Brown as shown on the wiring diagram to 7. When Brown goes live, the valve will close. This is obvious, of course, but impossible to find out in advance since the wiring diagrams only show the NC version (V4043H)

We haven't got the weather compensation in yet, but I've established that the boiler will set the flow to the configured flow temp when SL1 is live, but when SL2 is live, you will get 70 degrees - so it is working as I wanted to and I can have a reduced flow for my CH.

I haven't yet checked what happens if SL1 and SL2 are both live - I presume it will give me either 70 degrees or max(70, CH flow temp) - which will amount to the same thing for me.

Once the weather compensation is in, the CH flow temp should be reduced further according to outside temp. The weather compensation manual is rather confusing as it shows HW OFF wired up to SL2 in, whereas I currently have HW ON wired there. I may have to rejig my wiring - will report back.

[John Rumm]

I found it quite difficult to find boilers that support split temperature operation.

Y plan is certainly less useful these days. S plan is fine so long as you don't permit both demands to be active at any one time. (and S has the advantage that you can expand to S+ with multiple heating zones)

Yup Honeywell's own doc mentions both:

However the wiring plans shown (inferior versions of ours[1]) show the NC version which has two extra wires connected to the "end of travel" micro switch.

[1] Still perhaps they figure with only one function and one set of L & N wires in, there ought not be too much confusion as to what they do!

I would guess the DHW temp setting would take priority if both are called.

Might be interesting to add to the CH zoning article as an "application note" when you are done.

[Ben Blaukopf]

Yes. I do have the option of putting the loft on its own zone, but I think it'll be better overall to use programmable TRVs.

When I have some time, I will have a look at the OpenTherm stuff.

Indeed, it's pretty obvious when you get it out the back, but when you're trying to understand how it works before it arrives - not so easy!

Will do.

[Ben Blaukopf]

It turns out that when you add the weather compensation, the wiring changes in a strange manner.

Where previously SL1 was CH ON and SL2 was DHW on (and I tested this and it worked as you'd expect), the boiler now wants

SL1 is ON (CH or DHW, it doesn't care) SL2 is HW OFF (the complete opposite of previously)

If SL1 and SL2 are both GND the boiler still fires

I connected DHW valve (which is NC) open (orange) and the CH call from the Hive to SL1 HW/OFF from the Hive and Cylinder Stat satisfied to SL2

When I said that DHW call gives a flow of 70, I was wrong, it actually ramps up to 80.

With the weather compensation, flow temps on CH can be very low.

[John Rumm]

Yup, depending on the response curve selected, the flow temps on mine can be down in the 40s in the milder bits of the year. Just enough to take off the early morning chill!

Can you limit the DHW flow temp on yours? (doing so might make it possible to get condensing operation for most of the reheat - but at the expense of a slower recovery)

[RJH]

I've the same boiler (well, Logic 24+) and thought about this, but figured it might put undue stress on it as it didn't *appear* to be a design feature.

Also, at least IMHE, be wary of the weather compensation. As winter tailed out and it was still cool indoors, but 10C outside, the heating was very ineffective, with the radiators at c.40C. It might be that my house is just cold, or I bought a cheap (it was) and poorly designed unit. There's a picture of the slopes amongst the pics here:

Still, I'd be interested to find out how you find it - may well revisit. Washing up quantities of hot water are a pain as it is.

[RJH]

Oops, idiot that I am, that's a system boiler, mine's a combi. Of course it wouldn't work on mine. Probably ;-)

[John Rumm]

It is in theory possible to run a zoned DHW cylinder on a combi - and it would make some sense in a place like mine where the boiler is at the end of the house adjacent to the kitchen, and the bathrooms and cylinder are in the middle of the house. You could have an unvented cylinder near the bathrooms for high flow low lag delivery there, and the DHW output from the boiler to the kitchen for lower flow but again low lag and potable hot water.

The trick would be getting all the toys (i.e. controls) to play nice together if you want split temperature operation on top of weather compensation. I did toy with doing it on my setup, but could not quite convince myself that the Vaillant controls would cope (they probably could - but their system level documentation leaves a bit to be desired!) So I went with a system boiler in the end.

It sounds like you need to pick a steeper curve. On mine I think it came preset to curve 1.2, which would give a flow temp of 41-42 ish for a 10 degree outside temp, and I found that was not quite enough. So I switched it to 1.8 IIRC - and that gives a flow temp of about 46, which is enough IME.