Central heating problem

[m4tty]

Hi,

been asked to look at a friends central heating. It won't turn off. I know very little about central heating tbh and wondered if any one would be kind enough to tell me where to start. I would think the stat may be knackered. But how do you test it?

Thanks in advance for any pointers.

 

[m4tty]

Found this reply off the net.

LuckyDave (18:05 on Tue 06/Nov/07)

It sounds like the motorised valve is stuck open. If it too is a honeywell it will look like this http://content.honeywell.com/UK/homes/images/V 4043.jpg

Get a competent person to disconnect the orange wire, if that stops the 'constantly on' problem then fit a new motorised valve head.

Do you recon this may be the problem? Can anyone explain basically how central heating works.

 

[batty]

Testing stat take cover off identify live, switch live and neutral if there test live to neutral or earth should be 240v switch stat up between switch live and earth or neutral should be 240v and when clicked off should be 0 volts. More likely to be motorised valve. Get honeywell guide this has fault finding in it can be downloaded somewhere on forum.

 

[mikep]

Programmer sends live feed to stat if stat demands heat then energises motorised valve, valve moves into open position for circuit ( heating /hot water) pressing microswitch, switching on boiler/pump etc.

if valve seizes in open position microswitch remains on and boiler stays on heating/hot water gets very hot.

check valves move freely, then free off or replace.

Hope that helps.

Mike.

 

[PC Electrics]

Find the Honeywell site using your fave search engine. Then find the downloads section. You will need to register to use this section (that's why i haven't linked). Look for wiring info with either "issue 14" or "edition 14" (or similar, but it's defo '14'). This document has all the info you will need for all the standard plans, including an "electrical check" and fault finding page for each plan.

Also look for the product catalogue. This lists all Honeywells products, gives specs and internal wiring diagrams. V useful.

 

[m4tty]

http://www.honeywelluk.com/lib/pdf/Wiring-Guide-Issue-14.pdf

is this the one mate. Think so. Cheers

 

[PC Electrics]

That's the beastie. All you need in one place.

 

[batty]

http://www.honeywelluk.com/lib/pdf/Wiring-Guide-Issue-14.pdfis this the one mate. Think so. Cheers

They used to send them out but nowadays as people have computers you can download them and print them off.

 

[m4tty]

Programmer sends live feed to stat if stat demands heat then energises motorised valve, valve moves into open position for circuit ( heating /hot water) pressing microswitch, switching on boiler/pump etc.if valve seizes in open position microswitch remains on and boiler stays on heating/hot water gets very hot.

check valves move freely, then free off or replace.

Hope that helps.

Mike.

check valves move freely, then free off or replace.

How do you check valves move freely? 1st time dealing with these. Cheers

 

[kme]

Take the head off the valve (*its ok - no water comes out at this point {usually} ).

Stick a pair of pliers /fingers on the key, and see if it moves freely. If it does, it isn`t stuck!

You can also open the head up and check the return spring hasn`t stuck or broken.....

N.B. If this is a new install, then a common fault is to wire one side of the microswitch to the demand terminal - acts as a "lock on" once the valve opens - it won`t go off again.

KME

 

[m4tty]

Thanks for the help on this one everyone. If it is the zone valve stuck then why would the heating be stuck on if the thermostat was working and not calling for heat? Thanks

 

[Andy™]

if hot water is on, it will flow through the stuck open heating valve

 

[sparkytim]

The room stat controls the heating Zone valve which has an independantly powered contact in it. This contact has a PERM feed to it and when stuck on will give a PERM feed to the boiler and pump.

 

[SPECIAL LOCATION]

Thanks for the help on this one everyone. If it is the zone valve stuck then why would the heating be stuck on if the thermostat was working and not calling for heat? Thanks

Think of the valves as a contactor or relay....

energise the valve motor ['e.g. relay/contactor coil']

valve moves operates switch contacts, [relay/contactor operates switch contacts]

Switch contacts make or break to perform a function.

If valve stuck it will jam the contacts in the operated position...

the contacts will put the its own supply onto next part of circuit... (e.g. fire boiler & pump!).

Valves have a return spring for the motor that on some makes can become dislodged,

(e.g. some with plastic housings can have plastic spring locating lugs that break off),

so once the valve motor has been driven to the on position with a 230v supply, when the supply is removed the spring should return it back...

But if spring broken is off, the valve motor don't return to home position..

so switch contacts remain permanent ON... leaving a constant supply to fire boiler even if thermostat off or on!

HTH.