No central heating - HW only threewayvalve

Be recruited to sort out a problem on a friends heating.
My knowledge stops after gravity HW systems!
Their system has conventional boiler and programmer, cylinder thermostat and three way value (Pipe in - and the Port A heating, Port B HW - Drayton Flowmaster 2)
HW is OK
When Central heating is selected only HW heats - rads are completely cold - pipe work in airing cupboard is red hot.
if I push the little lever on the 3way over from HW to CH (very hard to push) and hold it then the rads get warm - when I let go again the valve moves back to HW and the rads cool.
I am guessing that it is the motor on the valve? Is this right? Could it be (or likely be) anything else? What would I need to test to find out?
If it is the motor? is this a standard part or does it depend on the valve? (in this case Flowmaster 2)
Can anyone help?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

are
Screwfix have one for around 9.50 is this the best price?

a
you
Cant be a jammed valve body as I can push the valve over to CH which works till I let go.
Was tempted to take my multimeter down tonight! As there is no room therm I guess that as long as the programmer "switches" the value it cant be anything else?
Does the tank therm affect the position of the valve? When it is set on HW&CH does the valve allow water to flow through both circults? or can it do HW only and CH only?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes.
A mid-position valve allows water into both circuits. A correctly installed diverter or "priority" valve would do HW only. The heads are different for the two types of valve, so buy the correct one.
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Ok - will check that as well

installed
Right will go an examine first!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

With a priority diverter valve, if the cylinder thermostat is locked on, and you have your hot water on, the central heating will never work. The boiler will eventually shut itself off when the return flow temperature rises. It will then cycle on and off.
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<snip>

<snip> This may be a warning sign. I have two seperate valves instead of a 3 way, but the mechanical part of the valve moves easily when pushed with the lever. If the mechanical bit is very stiff then it could cause the motor to burn out over time. Replacing the motor would then just be a short term fix, as the replacement would also burn out. However 'very hard' is subjective - steady resistance of a strong spring or almost needing a lever?
Christian seems to have covered everything else :-)
Cheers Dave R
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

replacement
I don't believe this is true. These brushless synchronous induction motors are designed to run stalled (what they do at one end of the travel). They will just do what they can. If the mechanism is stiff they will just sit there. The temperature they reach is determined primarily by the hot water in the valve. They do get "tired" IME due to changes in the magnetic properties of the rotors and need changing as they no longer have the push to overcome the spring.
--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<snip>

burn
Interesting point - my source was unreliable anyway (gas shop selling spare bits for pumps etc.). Thinking it through (I was told that if the valve was locked open permanently this could cause the motor to burn out) if the motor pushes the valve open and a spring pushes the valve closed then this should have no effect on the motor (apart from a brief spell of exitement the first time it tried to open the valve). Thanks for the info :-) Dave R
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.