Heatslave 18/25 central heating comes on independent of Honeywell programmer

Joined
28 Dec 2009
Messages
62
Reaction score
1
Location
Devon
Country
United Kingdom
Hi, we have an external Heatslave 18/25 and our central heating has been happily controlled by a Honeywell programmer for the last 4 years. At the moment we have been using the Honeywell it on its 'manual' settings where we set a target temp and if the temperature is too low on the CM927 unit, it sends a signal to the wall mounted unit, a green light comes on and the boiler fires up.

I'm not sure I have inadvertently 'done something' but on Friday evening I bled a radiator as it had been quite cool for a while. Heat returned to it so I went to check the boiler pressure and noticed it had dropped a bit so I topped it back up to the required pressure mark. All normal stuff so far.

At the end of the evening we normally turn the Honeywell to the 'off' position. That is what I did this particular evening and, as always, heating shut off and everything began to cool down.

When I woke the next morning the rads were hot, clearly on. Thinking I might have forgotten to turn the Honeywell unit off, I checked it and indeed it was off. I next checked the Honeywell receiver unit for the green light and that was off too. However, the boiler itself was on. I couldn't fathom how to turn it off so I switched the boiler off and on again and it immediately wanted to fire up. I turned it off and on again a couple of times and it still wanted to fire up so I left it and went inside. After a while it turned off by itself.

I noticed that the Honeywell could still control it using the manual settings and after a couple of tests to make sure it was firing up and shutting off using the Honeywell unit, I concluded it was maybe a glitch and now everything was ok.

Last night, I did the same, turned the Honeywell 'off', boiler turned off and I went to bed. This morning, the rads were hot again so checked the Honeywell and the receiver unit...both off.

I am guessing that, although I can still control the boiler using the programmer, it ALSO seems to be operating independently of it i.e. as if the programmer does not exist and maybe it is getting the message to fire up from the rad valves.

Any ideas what this might point to before I call the plumber out? This all started happening since I bled that radiator and re-pressurised the system.

Thanks

Dan
 
Sponsored Links
Thanks,

I was thinking this but on what though (boiler or Honeywell setting) and enough to heat the whole house to 19 degrees or so?

Even today, it has been coming on when the temp outside is well above frost and independent of the Honeywell controller which is set to 'off'. I have TRVs on all our rads that I have now set all of them to zero, just to make sure it isn't to do with the rads. Too early to tell though.

To be honest, the more I read up on this, the more confused as to how our central heating is meant to operate with this Honeywell, although in four years of operation you know when things behave 'differently'!

In our 3 bedroom house, we have rads in all the rooms bar the kitchen and utility room where there are spacesaver heaters. The Honeywell receiving unit is in the kitchen. ALL rads have TRVs bar towel rad in our bathroom. It always was my belief that the Honeywell could simply turn the boiler on and off using it's manual setting, and solely controlled the central heating. I have never seen the heating come on without the Honeywell receiver light being green. However, after doing a bit of reading I am beginning to wonder how the independent radiator TRVs work in relation to the boiler...could any of them make the call to the boiler to fire up or do they just control hot water to the rads according to each room's temperature so it is only the Honeywell that can ask the boiler to fire up the central heating?

Thanks

Dan
 
Sponsored Links
LOL, ok....how does one check for that and I'm guessing this is going to be on the boiler and not the Honeywell unit?
 
so I left it and went inside.

So your boiler is in an outbuilding... check the frost stat with a multimeter. If the light is off on the RF receiver and the boiler is firing. It has to be frost protection at fault!
 
Thanks, I'll check later. Yes, it is housed in one of those green cabinets outside of the kitchen. Out of interest, is my understanding correct between the rads/TRVs/Honeywell as above?
 
Without being there, we don't know what kind of frost protection has been installed. There could be several! Internal and/or external to the boiler and any of them could be at fault! Only fault-finding-procedures can pinpoint the defect! If you are competent with electrics and electronics, then you can test your way around the appropriate terminals during the fault period and conclude where the problem lies!
You 'could' identify the terminals into which any frost-stats are connected and remove them, in effect bypassing the component, during the 'nuisance' firing and determine if this stops it, then go to each stat that may be connected through those terminals and test at each component terminal block, one by one!
 
Manual TRVs will not fire the boiler.
Only the roomstat(s); cylinder stat and frost stat can call for heat.
 
This 'may' help you...

IMG_2197.PNG



And the full manual can be found here...
https://www.worcester-bosch.co.uk/p...-heatslave-internal-installation-instructions
 
Thanks, I have learnt a lot today! I'll check what I can and in all likelihood I figure I'll have to call the engineer out to properly sort it. At least I know what it probably is and what it definitely isn't!
 

DIYnot Local

Staff member

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

 
Sponsored Links
Back
Top