Fitting a usually open motorised valve to bypass

Hi guys,

So after a gorgeous summer I decided to to the unusual mod to my s-plan and as previously mentioned I have fitted a v4043B1257 usually ope valve on the by pass!

I now need to wire it up and due to my complete incompetence with a multimeter I thought I'd ask you guys the question, which is;

Should the live wire of the new valve be connected to the terminal of the orange cable from the CH motorised valve. I guess what I'm fundamentally asking is if the voltage on the orange cable is sufficient to power the motor of the new valve or if it's a lower voltage designed just to 'communicate to the boiler and the pump.

Look foreword to hearing.

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Yes, you could do that.

But normally open motor valves are not common.

What type have you found?

So I just did it and it worked! I realised that the orange is 240v as it powers the pump, logical I guess.

I'm expecting the rads to get hotter due to the improved modulating of the boiler which was previously confused by the hot flow slipping straight into the return without going through a balanced heat exchanger (I.e rad or HW cylinder).

What only just occurred to me is a secondary benefit, that being that with a grunions auto adapt pump, the pressure controlled pump will now work more effectively with greater pressure going through the CH system and more accurate pump modulation at low pump pressure due to less of the flow slipping through the bypass.

This is all very exciting!

If my logic is overlooking something that may result in my house exploding, I trust that your will spare my soul and let me know?

Just spotted your post. The valves a V4043B1257 as mentioned above. It's usually open. It has no manual lever probably because of it's intended purpose but that's not important I guess.
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They are not common because they are rarely used except for special applications.

But two ports of a three port valve can be used to achieve the same result with an industry standard valve available anywhere!

But I am still not clear how you are using it and why you expect it to benefit your system.

As far as I can see it will open when the pump stops ( if you have connected the pump to the orange as well ).

Normally though the pump will be connected to the boiler pump connection so that an over run is enabled. If that's the case they I agree that the bypass will be opened when the signal from the controls ceases.

Hi Tony,

On schematic diagrams I've seen online it sometimes appears that the pump live is connected to the orange of the motorised valve. In that case it would suggest that the valve would remain closed until the pump stops, but I think what you said in your last paragraph is the case with my system. The orange of the motorised valve signals the boiler to fire and the pump receives it's signal and power from the boiler. That would, as you said, mean that the bypass would open during the overrun.

I bloody hope that's the case, anyway! From what I can is! If it isn't then look out for my new thread 'which boiler to buy'
Hi tony,

You asked about the purpose and intended benefit...

Before, when I had the bypass always open, the water passing from the flow to the return via the bypass would increase then mean temperature of the return thus causing the boiler to modulate prematurely, particularly when most of the trv's are close so the ratio of rad return to the bypass is smaller. It was suggested to me to put a danios pressure valve on the bypass but this doesn't work with pumps that have proportional pressure such as the alpha 2L.

By fitting the usually open valve in the bypass the boiler doesn't modulate so quickly which means the rads get that bit hotter. The pump also get's quieter quicker due to 5litres per minute of water through the bypass which no longer flow

I think it's gonna work! Someone else did it to their system from my memory of a previous thread of mine and they had success.

Someone else did it to their system from my memory of a previous thread of mine and they had success.
Yep that was me. Must be over 8 years ago now. Same valve as you used without the operating lever or internal microswitch. I wired it across the orange switch wires so that it is powered closed whenever either the HW or CH valves open. Still working perfectly. It doesn't need a manual lever to open it because removing the power opens it. No need to worry about the current loading either. The valve motor is only 6 watt, a lot less than the boiler (and possibly pump) that are also connected to the same wire. To put it in perspective the microswitch and wires are rated at 2.2A (approx 500 watts)

I have written on mine in felt tip pen "By-pass valve normally open" to assist a new homeowner should I ever move house. They are pretty rare & mainly used with solid fuel systems for safety I believe.
That's right.

A solid fuel system needs a gravity flow to keep the boiler safe if the power fails and a pump cannot create a flow through the boiler.

The number sold must be fairly small though.

I'm a little gutted to be frank. My ego would have quite like to him of itself as pioneering!

So the improvement has exceeded my expectation. It's a must as far as i concerned.

The lever's just useful for a quick check to see if the valve is active I.e a baggy lever.

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