HELP NEEDED PLEASE!! C/W not working but water hot!!

[8valverpaul]

I know this has been asked before but wanted to tell you the specifics!!
I have a boiler that fires up fine (when the controler tells it to), BUT turns off about 2-3 minutes later?!?!?!?
The water is boiling hot but no hot water through the rads??
I've been told to replace the old Myson pump, but I was wondering what is causing the boiler to shut off??
Dodgy R/stat, pump or tank stat??
I am an electrician so not a fool (matter of opinion I know ), but this is baffling me!?!?
Can you help??

 

[scatmanjohn]

Sounds like the pump.

 

[8valverpaul]

Could you tell me why please mate?? Is is just free-running and not PUSHING round the system for example??

 

[scatmanjohn]

Is the pump running (240vac)?

Are you saying that you can get hot water ok?

 

[Gasguru]

If pump is not running or it is running slow it will not transfer heated water from boiler.

Is it an old Myson Plan pump?

 

[8valverpaul]

The Pump is a Myson Compact and IS running!! I can get hot water ok yes!!
I'm gonna try holding the MV in manual and boiler stat down and tank stat up as advised in the FAQ's, does this sound about right as a 1st port of call??

 

[Gasguru]

Are you sure the immersion heater isn't heating the hot water cylinder?

In hot water mode do the pipes around the pump get very hot?

Have you checked the radiator valves are open (thermostatic valves can stick during the summer).

 

[8valverpaul]

Are you sure the immersion heater isn't heating the hot water cylinder?

In hot water mode do the pipes around the pump get very hot?

Have you checked the radiator valves are open (thermostatic valves can stick during the summer).

1st) Yes, the immersion is OFF!!
2nd) YES, bloody boiling!!!!
3rd) Yes mate they are all on!!

Any more info??
I've just done the test as I said abpove and the rads are now getting warm, so does this mean its the motorised valve thats knackered?? Would you still advise a new pump also??

 

[Gasguru]

With the pump turned off unscrew the black plastic hex nut in the center. Once its unsrewed pull it gently whilst rotating and it will lock into the impeller. There may be a little water loss. Now run the pump. Grip the hex nut with you fingers. If the pump is turning OK the pump will be difficult to slow.

 

[8valverpaul]

Done that and I could'nt stop it turning (running in position 2), does this mean its fine and I just need an MV??

 

[Gasguru]

The impeller could be sludged up or sheared off so not 100% conclusive the pumps stuffed but assume the pumps OK for now.

Do you have a single mid-posistion valve or 2 zone valves?

 

[8valverpaul]

Looking in the 'Definitions' section, I have a 3 port/diverter valve!!
Its a Honeywell V4073A1039 (telling me to use a 40003916-003 to replace the head), does this sound right?? Whats your verdict then mate??
All your help so far is much appreciated by the way!!

 

[Gasguru]

When the hot water is selected the motorised valve will sit in its rest position the water flows to port B. When heating only is selected the valve motor should move the valve ball to allow water to flow out of port A. In this position the lever should have no resistance on it.

If the system is wired up correctly the boiler and pump are only switched on once the valve has fully open port A.

 

[8valverpaul]

I've followed the procedure in the FAQ's and put the MV in the manual position, i've turned the tank stat up and turned the boiler stat down and i'm getting warm rads!!
This is the 1st time since I started trying to sort this out that we've had warm rads, i'm assuming this means I need a new motorised valve??
The boiler keeps coming in every now and then for a few mins.
Does all this sound right??
On my system the hot water needs to be selected WITH my heating on the programable timer.

 

[Gasguru]

A mid position valve should always allow flow since one port will always be open.

The whole point of having a mid position valve is that each zone (either hot water or heating) can be selected individually or both at the same time. Appears your system is not wired correctly and may have the timeclock set up incorrectly. This is quite common with these valves.

Turn the cylinder stat down and the room stat up and select the heating and hot water. The valve motor should allow flow to port A and the lever will have no resistance. If this doesn't happen the motor may be dead.

This however still doesn't explain why there is no flow when the heating is selected.