Central heating doesn't work but hot water is ok

[Sausage]

The overflow is not of concern to the person who has the problem at the moment.
I was only trying to give as much information as possible, just in case it was related to the heating problem.

Thanks for the replies.

 

[Agile]

I have a Potterton Suprima 80 boiler. Lately my central heating wont come on

Since its YOU who have the problem then that person is clearly YOU !

A dripping overflow is an environmental nuisence apart from wasting water contrary to the Water regulations.

Advise me of thre address so I can ask the water Supplier to serve a remedial Notice.

Tony

 

[Softus]

Would be grateful if anyone has any advice.

In view of your approach to this set of problems, my advice is that your client ought to find themselves a competent heating engineer.

 

[christopher12345678910]

all i did was drain water out my boiler so water pressure was empty then emptyed all radiotors with drain valve then closed drain valve then i topup the water pressure with the water pressure valve located under neath my boiler i toped up the pressure up to 2 psi and then set the thermostat to full then it worked again my boiler

 

[AlfaIan]

without knowing what is connected to what at the terminals your measurements don't mean much.
Beside any earth and neutral wires your MZV should have 3 other wires.
These are usually white, grey and orange wires (if its a modern 3 port valve). The room stat, when turned up should make the white wire live and confirms everything ok up to the MZV.
It's the white that drives the motor over the first half of the full range
If you set the programmer to HW only all power to the motor is removed and the motor unwinds to the rest position by the return spring.
If you now put programmer to CH only the motor should move and you should be able to hear it move or if you have the head removed you should be able to see it move.
When the valve reaches mid way, power is switched from white wire to grey wire. motor then continues along second half of range.
During the second half a micro switch is operated and allows power out of the MZV through the orange wire to light boiler.
Question is? is the motor moving or not. and dont forget a stiff spindle could also be the cause.
So its, power at the white wire? remove head stiff spindle? does motor move to CH position? if not replace motor if it does micro switch faulty replace actuator head.
I would not worry about the buzzing sound. In the CH only position the motor comes up against a stop so although it's not turning it is energised to keep it there.
Likewise in the mid position a modified voltage holds the motor against the return spring.

Sorry to drag up an old post. I'm having similar issue to this.

CH not switching on, but HW is. Mixing valve is energising, with HW program ON holding mixing valve to CH position radiators get hot. Bled radiators but no air trapped.

Also checked voltage at junction box but getting no readings (more than 2-5v) but think that might be my meter as the mixing valve and pump are working.

Only other comments is a couple of times when when CH was working it tripped out the house circuit breaker. Both times happened when CH was ON and the programmer turned on the HW.

So have I blown a fuse? or faulty micro switch in the mixing valve motor?
Can I link the orange wire to the white or grey wire to bypass the micro switch to see if the boiler starts up?

Ian.

 

[AlfaIan]

Done some more testing. Had the CH ON for an hour (programmer running HW & CH for 1 hour)

Also discovered two levers a metal one and a plastic one (I was only using metal before) but the plastic has a bit more travel to work the relay so I kept working that open/shut which felt easy enough no sticking points.

Put the mixing motor head back on and can hear the limit relay clicking open/shut every few seconds. Still wont run on CH only program though.

 

[MANDATE]

It appears you can get ch along with HW but not CH only.
So it's one of two things.
The valve is not moving from mid position to CH only position. This is caused by either no power on the grey wire or micro switch No 1 is faulty.
Remove the head to see if valve moves from mid position when you turn the HW off having had both CH and HW on together

If the valve does move to CH only position, then the second micro switch which allows power out from the valves orange wire is faulty.

 

[AlfaIan]

Hi Mandate.

Thanks for the information. I see if I can borrow another voltmeter from work so I can check voltages on the wires you mention and get back.

 

[AlfaIan]

Might of figured out the reason. Took the micro switches out and looks like the track from the bottom relay to the orange wire has rubbed off over the years.

Untitled

• AlfaIan
• 12 Jan 2014
• 1

Now to figure a fix.

 

[MANDATE]

I reckon power on the white wire must be OK, otherwise the valve would not move to mid position. Same with the motor.
There are two micro switches, each with two sets of contacts.
(a) Switch 1... 1st pair of contacts: power from white wire goes across these closed contacts to drive motor until micro switch is triggered at mid position.
(b) Switch 2... 1st pair of contacts: power from white wire goes across these closed contacts to a PCB to produce a modified voltage to hold the motor/valve at mid position (if needed)
(c) Switch 1... 2nd pair of contacts: When switch is triggerd at mid position, these contacts (previously open) become closed when the 1st pair open. This now allows power on the grey wire to drive the motor forward to the CH only position
(d) Switch 2...2nd pair of contacts: When switch is triggered just after mid position and the modified voltage is not needed these contacts (previously open( become closed and the power (from white wire) is now available from the valves orange wire to light boiler.

So failure of valve on first half:
No voltage on white wire.
Faulty motor
Faulty M/S 1 (a) above

Failure of valve on second half:
No voltage on grey wire
Faulty M/S 1 (c) above
If valve moves correctly, faulty M/S 2 (d)

 

[MANDATE]

When I had the same problem it turned out to be burnt contacts on 2nd micro switch.

 

[AlfaIan]

Hi Mandate

Got my voltmeter to read voltages (I had it on auto which doesn't automatically detect AC )

I'm getting
White = 240v
Grey = 240v
Orange 55-60v

Measuring the voltage on the back of the second micro switch I get 60v middle pin (directly linked to orange). Both other pins I get various voltages so guess meter isn't detecting a voltage. I get this in both open and closed positions.

Does that sound like faulty micro switch? or a break elsewhere on PCB?

Ian.

 

[AlfaIan]

Traced through the voltage.

Goes through the first micro switch okay, goes through a resistor then to a diode and this is where the 240v stops so looks like a faulty diode. Could explain why it tripped the house electrics if the diode was breaking down maybe.

Problem is I cant tell what number is on the diode, anyone know the part number for the diode?

 

[Dean744PiN5]

They dont sell parts for these pcb's on their own. So its a new actuator head, or maybe a trip to maplins if you really just want to repair the pcb.

 

[AlfaIan]

I think I've sorted it. Turns out a track on the other side of the PCB had also wore off meaning no voltage to the second relay.

So repaired that track as well as the first one and appears to be working now. Just need to see if it carries on working with the switching between HW/CH and both.