CH goes off with HW but comes if lever is pushed

[Palmist]

Hi Guys,

I had the classic case of hot water and CH but no CH on its own. After much research and useful helpful on the forum, I ended up replacing the motor Head. Now CH comes on its own and stays on for as long as I want. However if turn HW on with the CH it goes off when HW goes off. I then have to go up to airing cupboard and push the lever on Honeywell 4073 valve lever just a little bit [very tiny bit] and boiler comes on again.

So looks like valve is working but might be something not clicking fully somewhere. When I was replacing the motor head, I did check that the valve was moving fine in either direction.

Now I can probably live like this but I am concerned if this will break and turn in to a major issue if not fixed.

Y Plan System

Worcester Greenstar Ri Condensing Boiler

Honeywell 4073 Motorised 3 port Valve.

thanks

 

[seco services]

Sounds like the valve is slightly sticking when ch only port is opening so not quite activating the micro switch.

 

[Palmist]

Sounds like the valve is slightly sticking when ch only port is opening so not quite activating the micro switch.

Is it worth replacing the valve itself or do you think taking the motor head out and putting it back again might resolve the issue.

 

[MANDATE]

Are you sure both supplies that feed power to the grey wire of valve are in place.
The wire from programmer HW OFF must be there cause you get CH only.

But when HW is on and becomes satisfied, the cylinder stat provides the power from the satisfied terminal to move valve forward. If that wire is not there or not connected then valve stays at mid point and the micro switch that provides power to light boiler does not get activated.

 

[Space cat]

However if turn HW on with the CH it goes off when HW goes off.

When you say "when HW goes off", do you mean that it goes off because the cylinder stat says it's hot enough? What happens if you don't wait for this but turn HW off at the controller?

 

[Palmist]

However if turn HW on with the CH it goes off when HW goes off.

When you say "when HW goes off", do you mean that it goes off because the cylinder stat says it's hot enough? What happens if you don't wait for this but turn HW off at the controller?

either. as soon as HW is off either through program or manual it will knock CH off as well

 

[Space cat]

Here's what I think is happening though I'm not sure exactly why.

Starting with everything off, you switch CH on. The CH-ON voltage from the controller (coming via the room stat) drives the valve to its mid-position (HW and CH both on) but the boiler doesn't start yet. Inside the motor head, two switches operate. One opens to reduce the motor power to a low level, just enough to hold the valve against the return spring. The other switches closes.

If, and only if, you also have a HW-OFF voltage coming from either the controller or the tank stat, that second switch connects it through to the motor which now drives all the way over to the CH only position. At this point, a third switch closes and connects the CH-ON voltage to the boiler, which finally lights.

So far so good, the valve has done exactly what it's supposed to do. If you listen to the motor during this time, you'll hear it turning as it moves the valve but the boiler will only come on when it stops. As long as you have HW-OFF, the valve will be held in the CH only position and the presence or absence of CH-ON will control the boiler.

Your problems begin when HW-OFF is replaced by HW-ON. At this point, HW-ON supplies the boiler, just as it does when you want HW only. It has a direct connection. Meanwhile, with HW-OFF gone, the spring pushes the valve back to it's mid-position. (You should be able to hear this.) Everything appears to be fine in that you have both CH and HW - and yet something in the motor head isn't right!

My best guess is that the valve has run back just a little too far. Remember those two switches that operated when CH-ON originally drove the valve to mid-position against the spring? One of them closed, allowing HW-OFF to drive the valve all the way over to CH only. I think that one has opened - though it shouldn't have. Meanwhile, the other one, which dropped the motor power coming from CH-ON to a low level, is still open. The valve is sitting in limbo, held just short of mid-position. You will have CH for as long as HW-ON powers the boiler but HW-OFF cannot drive it over to the CH only position - not until you give that lever a very slight nudge.

If you can confirm all this by careful observation of - and listening to - the valve as it goes through the sequence CH only -> CH+HW -> CH only -> nudge lever (while also watching what the boiler is doing), it's a pretty fair bet that the new motor head is faulty.

EDIT:

I just thought of this last night: what if the HW-OFF and CH-ON connections were crossed over at the valve? Thinking about it, a lot of things would still work as expected.

1) HW and CH both off: The valve sits in mid-position, driven there by HW-OFF, but the boiler doesn't light because that requires either HW-ON or the valve right over to CH position.

2) HW only: HW-OFF disappears, allowing the valve to run back to the HW only position. (You can listen for this.) HW-ON lights the boiler.

3) CH only: HW-OFF drives the valve to mid-position and CH-ON takes it on to the CH only position. That's the wrong way round but so what? As far as the valve is concerned, it's just two wires with volts on them. It's now HW-OFF that powers the boiler but this doesn't matter because, when the room stat removes CH-ON, the valve drops back to mid-position and the boiler goes off.

4) CH first, then HW: CH-ON is holding the valve in the CH only position. HW-OFF, which was powering the boiler, has gone but HW-ON takes its place. You will only get HW by leakage past the valve - until the room stat cuts off CH-ON, which leads us to ---

5) HW first, then CH: This is your problem condition. The valve is in the HW only position so CH-ON can't get past that switch in the motor head; not until somebody pushes that lever.