VCW 242 EH Diverter question?

[paddy69]

Hi!
Does someone out there who knows these old boilers tell me, if I draw hot water, should this cause the diverter to move into DHW position regardless of whether the micro switch clicks in?? In other words, is it purely hydraulic action that moves the diverter valve into place???
And, if this is the case, is it the servo valve that will likely be at fault (or one of the small tubes from it blocked?) if diverter not going itto DHW mode?
The diverter has been cleaned and a new diaphragm put in so I am sure that works fine.

Thanks!

Phil

 

[DP]

Phil, this beastie is a tricky boiler.
Best to call in someone who knows this boiler

 

[Gasguru]

The diverter operates on differential pressure developed across the pump.The servo valve just applies this pressure one way or the other to the diverter depending on a DHW or HTG demand. The water section must operate correctly to turn the cam sufficient to fully operate the servo valve. If the DHW microswitch is not operating start by checking/replacing the water section diaphragm.

 

[paddy69]

Thank you!
The DHW microswitch is operating fine! There seems to be plenty of movement on the cam. It is the diverter valve that is reluctant to move out in DHW mode. In fact, the microswitch will operate and the boiler will fire but seems to go into HTG mode with the shower on (it draws less pressure of water) A hot tap fully on will cause the diverter to properly move into DHW mode.
(Mmmm! Given it some thought. It must just "appear" that lower water pressure when drawing DHW for shower doesn't move diverter valve. BUT the servo moves OK and trips the micro switch.(that is the part the DHW pressure drives) It must then be up to the pump to cause pressure to move the diverter valve)

 

[DP]

Phil, where is this HW microswitch located?

If I remember correctly, this boiler will not move diverter to CH position if hot water is demanded.

 

[paddy69]

It's on the back of the servo valve, on top of the water section!
Yes, if the HTG is on, water flow (drawing DHW) through the water section operates a rod that moves a cam that trips a microswitch and should feed water through the servo valve to one side of a diaphragm in the diverter valve. This should move the valve outwards to release both microswitches on the diverter.
There is nothing like a simple boiler, and this is nothing like a simple boiler, but has been very reliable.

 

[DP]

The diverter sits in mid position when no demand
For CH, timer, programmer or whatever, starts the pump running
Would have to check my notes, but suspect diverter spindle retracts because high pressure to right and low pressure to left of diaphragm results in said direction of travel

For HW, the cam moves to water section pin ejection, microswitch is operated by the cam, thus in turn runs the pump, now flow to two sides of above diaphragm is reversed (to that of CH run) and diverter spindle moves to the right

Hope I am not wrong as I have not looked at this boiler for a while

 

[paddy69]

Yup, that is my understanding of it. Just confused why, on occasion, when drawing HW, the microswitch is activated, pump runs, but diverter doesn't always push OUT for DHW. Sometimes it even draws IN and CH runs! MUST be something in the servo not diverting the flow to diverter correctly!

 

[Gasguru]

It could be a worn DHW diaphragm, trapped air (check the auto air vent behind),badly adjusted pushrod, failing servo valve (sometimes full of crud and the ceramic discs can let-by), partially blocked control tubes, blocked orifice on the banjo bolt....and sometimes you'll find there is a tiny spring valve assembly on one of the control tubes that blocks(rip out the inards below) etc etc.

Untitled

• Gasguru
• 16 Feb 2013
• 2

 

[AGAS]

,

If I remember correctly, this boiler will not move diverter to CH position if hot water is demanded.

i think the valve returns to ch after a dhw operation.

just some suggestions :
small tubes & filters need cleaning also maybe check the needle valve re check diapm , the pin comes out quickly for HOT to the right and CH moves slow to the left ( maybe wrong boiler ) and maybe check the water section or venturi for cr&p , and as gasguru has said the pushrod can be dislodged but struggling to remember anything else about that ,just some suggestions while your in there , if you dismantle the diverter valve all washers should be changed ( been caught on that one ) . the bunnies will probably know and I'm interested to know the answer as well TBH , only worked on this boiler twice .

EDIT probably better to change the diverter if still available but clean other connecting things ( mentioned above ) as well

 

[Agile]

Chris Hutt in Bristol used to love this model and could describe how they worked very eloquently.

Sadly he is no longer with us!

 

[DP]

i think the valve returns to ch after a dhw operation

You are right Agas. My wording wrong.
What I meant to say, diverter sits in mid position which is the rest position. Of course it will position for CH after hot water demand finishes if CH demand active

 

[paddy69]

blocked orifice on the banjo bolt....and sometimes you'll find there is a tiny spring valve assembly on one of the control tubes that blocks(rip out the inards below)

Can you point me in the direction of these? I think my problem may lie with one of these.

 

[Gasguru]

Label up and then pull out the servo valve, water section and control tubes....almost guarantee somewhere in that lot you will find the problem. I hope you have the manual....it gives the measurements for setting the pushrod and microswitch.

 

[AGAS]

water section and control tubes

ye deffo agree they can get shyte in them ,

setting the pushrod

didn't know you had settings on it but good to know