Worcester Greenstar Heatslave 18/25 EXT - Controls not working

23 Feb 2016
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United Kingdom
Hi. Just moved into a new cottage. Boiler fires up great and has the radiators and hot water pretty hot and quickly. I've realised though, that the controls don't seem to be working.

1) There is a room thermostat, which does click on and off but doesnt seem to affect the boiler in any way. I can still hear it running when it clicks off for example and temperature doesnt change. - How can I check to see if its wired to the boiler and if so what might cause its lack of effect?

2) I wanted to change the temp of the hot water (DHW), I turned the dial down on the boiler but it had no effect whatsoever. Its right down at minimum and still as hot as it was (too hot!). What's likely to cause this? Recommendations before I call an engineer?

3) The Central heating control (CH) seems to work and when I turn the dial towards minimum the boiler cuts off as though it doesnt need to draw heat whereas the DHW doesnt react like that. I'm guessing this shows it is working and only taking the CH upto the controlled setting but I have no idea how to be sure.

4) I can see the Diverter Valve (Drayton Hansen Class F) moving. When I turn the boiler off / on the switches all move so I'm guessing thats a good sign but I dont know about these things.

So at the moment, I have heat and hot water but seemingly no way to control them which I guess is dangerous and inefficient. Before I call out an engineer I'd love some advice / things to consider / check just so I know what the score is. Looking forward to hearing your thoughts! We seem to be getting through a hell of a lot of heating oil!

Cheers Adi
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On what basis have you "just moved in" ? Bought it ? Renting it?

Do you have a hot water cylinder?

I suspect the boiler may be ( or be connected as ) a system boiler and that the hot water knob is not used in your setup.

My view is that you need an engineer to service the boiler and explain the system and controls to you.

Hi Tony thanks for the swift reply.

Yes I've bought the house. Its an old cottage but the central heating is relatively young. No hot water cylinder. It has a Drayton Control unit LP722 on the wall which has a facility for hot water control / boost / timer etc which I guess is redundant and inly used to control the timing of the CH? Would that sound right? We have it set so water is off. Heating is on timer and we use boost when we're in and cold. Not sure if thats right!?

I'm definitely up for getting an engineer to service the boiler so we know where we are and show me the controls. Totally agree. Just though I'd try and get some idea of it all before hand so I know whats being explained ;)
Is this Drayton diverter valve inside the boiler?

If there is no hot water tank anywhere ( including the loft ) then it must be a combi and the hot water knob would be expected to work.

An engineer should be able to check everything and advise you. It may well have a fault in relation to the hot water.

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Yes the Diverter valve is inside the boiler housing. We have no loft (its rooms in roof). It is a combi (Worcester Greenstar Heatslave 18/25 EXT combi condensing).
I would have expected the controls to work. Otherwise there is no way of controlling tap temp. As I mentioned the Room Thermostat has no effect either so there's at least 2 issues in relation to control. Hot water and Heating. Cheers
I would also agree but it does need to be checked.

Worcester seem to have produced several models with no control on the hot water temperature.

The presence of a knob is not relevant in all cases!

Yep will defo get it checked, as I said, just trying to see if any one has any experience of this so I might gain insight before I get an engineer out. (not instead of).
As a combi, the boiler will fire randomly to maintain the temperature of the heatstore, so the boiler firing when the heating is turned off is probably correct. Also, a combi gives priority to DHW so if there is a DHW demand, the heating thermostat will have no effect until the heatstore is up to temperature.
The hot water knob controls the temperature of the heatstore and adjustment may not have an immediate effect. It would be prudent to arrange for a service, and check over as it may not have been done if the previous owner knew he was selling. You can voice your concerns to the technician then.
Thanks for your reply. I understand what you;'re saying about latency. That makes sense. However, the hot water control has been on minimum all day and still scorching hot and the room thermostat is also at mimimum and the radiators are still cranking at full power. So it doesn't seem to be to just be lag but complete lack of controls.
Is there a frost stat overriding the room stat? You need an experienced eye to look at it. Diagnosis of such vague symptoms is difficult without being able to follow a logical sequence.

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