Converting a V4043H1056 (NC) 2 Port Valve to a V4043B1257 2 Port Valve (NO) ??

4 Jan 2008
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United Kingdom
Hi there !

I am planning to reconfigure my domestic central heating and hot water system.

I need to convert a normally closed V4043H1056 2 port valve to a normally open V4032B1257 2 port valve. I appreciate that there will be wiring changes required as the normally closed 2 port valve does not incorporate a microswitch.

What I wanted to confirm is whether this is possible, that it is simply a matter of changing the powerheads ? I am assuming that the actual valve body it is the same in both of these 2 port valves ?

Many thanks.
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I believe it's the other way about, the 4043H (NC) is a 5 wire lead and incorporates the switch, the 4043B (NO) is a 3 wire and doesn't. My understanding is that the valve itself is the same but not sure if the head fitting is the same, have never swapped them over but it would make sense that it is.

Basically, when power is applied to the 4043B then the valve closes but it's fail safe position is normally open, more so used with solid fuel heat sources etc where an open fail safe is required. Can't see why it couldn't use the same energising power wiring as the 4043H, but it all depends on how it is to be implemented.
Hi many thanks. I spoke to Resideo Honeywell Home heating controls and they said that they do not make a replacement head for the V4043B1257, which seems odd in that if it fails e.g. the spring gives up then it is a complete new valve ?? Odd ? I appreciate the motor inside can be easily replaced.

What I was planning to do was reconfigure my system to provide priority DHW - there are a couple of ways that I can do it, based on my system configuration, one way was to re-configure the V4043H1056 ( NC ) to become a V4043B1257 ( NO ) and re-wire accordingly.

So when DHW comes on ( at the programmer ) and the cylinder stat is not satisfied, then the NO 2 port valve will close therefore circulating all the flow water around the coil in the base of the DHW cylinder.
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You can convert your standard NC motorised valve to an NO valve very easily - since it isn't a safety-critical valve just supply it via a relay wired so when relay input is high relay output is low and vice versa.
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Hi it is an unvented cylinder, however it has it's own 2 port NC valve installed as per the manufacturer's instructions.
I am surprised that if it's on an S Plan already that it has another 2 port, presume it's tied into the HL. Strictly speaking it is the correct use of a secondary 2 port for an unvented regardless of the plan, it's added as a fail safe. Normally though the usual approach is that they are only added when it's a Y plan.
This schematic might be of some help but only uses the NC motorized valves, with the addition of a NC relay?.


  • HW Priority Diagram.pdf
    882.7 KB · Views: 98
@WhatNext did you ever manage this? I'm looking to do the same and was looking for alternatives to the V4043B but it looks like there aren't any.
Why can't you use your existing NC valves and add that NC relay as in the schematic?.
Wiring for PDHW with a NO zone valve is much simpler than a standard s plan with an additional relay.

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