Heating only on when HW is on

monkfiish · 29 Oct 2004

Hi

My Gas Central Heating has developed a problem whereby the boiler (NOT a combination boiler) will only ignite when the hot water is on - i.e. if I set the water tank thermostat higher, then the boiler is on more & I have a hotter house.
My CH system is pumped, and the pump is running OK.
The room thermostat seems to have no effect - if the HW is not firing the boiler, then turning up the room stat will not switch the boiler on. The room thermostat makes its usual faint click, but I guess that this message is not getting to the boiler !
Is the room thermostat the most likely failure point, or are there other things I should check ?
I'd like to be armed with an idea of the possible causes & costs before an engineer arrives.
All comments very gratefully received !

Thanks.

ArtfulBodger · 29 Oct 2004

monkfiish said:
The room thermostat makes its usual faint click, but I guess that this message is not getting to the boiler !

The room stat sends the message to the motorised valve, which is supposed to relay it to the boiler. Yours doesn't seem to be doing so.

Depending on what sort it is and what the problem is, you might be able to get a replacement motor, a complete head assembly. Or, if your are unlucky and have a blue switchmaster, then you will need a different manufacturers valve, wiring and pipework changes.

Nip up to the airing cupboard & tell us what you have in there.

MANDATE · 29 Oct 2004

Hi Monkfish! Just dealt with a similar problem. Central heating ok as long as it was sharing with hot water. But when hot water was satisfied heating would not work alone.Roomstat proved to be functioning.
The head was removed from the motorised valve and observed and the actuator did move to the central heating positon but no voltage on the 'orange' wire. This proved the motor was ok but the 2nd microswitch was the possible cause. With actuator stripped down a test proved microswitch at fault. microswitch de-soldered from circuit board and opened up. contacts removed and cleaned.All back together now and functions on my home made test rig. Cost wise it will be cheaper for you to replace the whole actuator head.

ChrisR · 29 Oct 2004

Artful - and anyone: I have some new and used switchmaster 3 port valves/actuators.

ArtfulBodger · 30 Oct 2004

ChrisR said:
Artful - and anyone: I have some new and used switchmaster 3 port valves/actuators.

Thanks Chris I wish I'd known this before as I've got a Switchmaster to Honeywell conversion to do on Monday. When I come across one again I'll give you a shout.

AB

P.S. Just how big is your van??

monkfiish · 1 Nov 2004

honeywell. A Honeywell 3 port valve (according to various websites). The room thermostat is also Honeywell. No serial numbers to be found though.
Is that pretty standard ? The only other thing visible is the maze of cables that I'm certainly not going to be tinkering with - everything looks to still be connected though!

Am I looking at a costly call-out, do you think ?

BTW - I'm really impressed with the friendly responses on this board - Thanks !

ChrisR · 2 Nov 2004

If you have 1 valve it'll probably be a 3 port (Y plan), if 2 then 2ports, (S plan).
See the honeywell site.
Fairly simple to change a head yourself though we're still not sure exactly what's wrong with yours - depends on type.

monkfiish · 5 Nov 2004

yup - it's a honeywell 3 - port valve. Looking at the web these are quite pricey - do you think this is the most likely point of failure ?

ChrisR · 5 Nov 2004

If it's a normal Honey (4073) then its starting position is to the HW, and it motor opens it to hw + ch then ch only. They return under spring pressure. If your rads get warm when the HW is on (without the ch), it must be partly open.
Check on the end of the valve head that the little lever is not on the hooky bit - which will hold it part open ("Man").
If you fancy sliding the head ccover off (one screw to loosen) you'll be able to see the internals and by shoving the leversee how it should move. On CH only the valve mechanism should go to the end of its travel.

If the motor doesn't turn at all a new motor is £15 or less in the "sheds". If the head's sticking it comes off with 2 screws AS LONG AS THERE'S A PIMPLE ON THE COVER. The early ones without the pimple don't come apart "dry" so you'll need a whole new valve - and a drain down.

If you're handy with a multimeter you should check first that the motor's getting the right signals- white and grey wires both 230V for CH only. And the orange one, which turns the boiler on.

Wiring diagram here http://content.honeywell.com/uk/homes/Catalogue/Sundial Plans/3.4 Y Plan.pdf

A new head costs almost as much as a whole new valve. I can sell you one for £35 inc post but it'll take a day or two to get to you. Email addy in my profile.

misternomer · 15 Oct 2005

Hi Chris,

Don't suppose you have any of those Blue switchmaster actuators left do you? Just got back from holiday and it looks like the plate at the back of mine had rusted through and the spindle connecting to the valve body has now worn out. I could probably get away with a new backplate and actuator and leave the valve body as it is. I really don't fancy wasting my weekend doing a Honeywell conversion.

Otherwise - can you suggest a close replacement that won't need the pipework to be modified? It's a 3 way valve, by the way. I have a Potterton Flamingo boiler, hot water tank and Honeywell programmer. There is no thermostat anywhere in the house and the heating only comes on with the hot water.

Cheers

Richard

Sel · 15 Nov 2005

Can anyone help me find a dreaded Blue Switchmaster Actuator. The valve appears fine - just an electrical fault on the actuator I think. Cheers

dannyclark · 7 Jan 2006

ChrisR said:
Artful - and anyone: I have some new and used switchmaster 3 port valves/actuators.

waynester · 30 Jan 2006

Hi chris, do you have any more of the switchmasters, am in worthing,
thanks

wikey · 21 Apr 2006

hi Chris
further to your post on this subject

the link to the honeywell page seems to be dead any where i can get more details on this valve? i have one a few years old and i am suspicious that it is causing problems with my system.

i am part way throu checking all wiring but need details on the valve function and wiring to do the next bit of the checking..

cheers
mikey

ChrisR said:
If it's a normal Honey (4073) then its starting position is to the HW, and it motor opens it to hw + ch then ch only. They return under spring pressure. If your rads get warm when the HW is on (without the ch), it must be partly open.
Check on the end of the valve head that the little lever is not on the hooky bit - which will hold it part open ("Man").
If you fancy sliding the head ccover off (one screw to loosen) you'll be able to see the internals and by shoving the leversee how it should move. On CH only the valve mechanism should go to the end of its travel.

If the motor doesn't turn at all a new motor is £15 or less in the "sheds". If the head's sticking it comes off with 2 screws AS LONG AS THERE'S A PIMPLE ON THE COVER. The early ones without the pimple don't come apart "dry" so you'll need a whole new valve - and a drain down.

If you're handy with a multimeter you should check first that the motor's getting the right signals- white and grey wires both 230V for CH only. And the orange one, which turns the boiler on.

Wiring diagram here http://content.honeywell.com/uk/homes/Catalogue/Sundial Plans/3.4 Y Plan.pdf

A new head costs almost as much as a whole new valve. I can sell you one for £35 inc post but it'll take a day or two to get to you. Email addy in my profile.

dillon g · 24 Sep 2006

____________________________
lynda, moderator

Post locked, see forum rule 20

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Heating only on when HW is on

Similar threads