DIY Doctor

Main navigation

Hot water but no central heating

Postby SidewaysMatt » Thu Aug 23, 2007 9:29 am


I've developed a problem with my central heating. It's a fairly new house (3 years old), and I have a Worcester Greenstar condensing boiler.

I've always had the CH and HW set to permanently running on the programmer in the airing cupboard, and then flicked the heating on when needed using by using the room thermostat in the living room.

However, it's now not working! If I turn the room thermostat, it clicks but the boiler and heating pump etc don't fire up.

The boiler itself still works as I still have hot water no problem.

The obvious thing to me would be that the room thermostat is broken, but could it be something else?

How do you test the thermostat is switching properly?
Rank: Labourer
Progress to next rank:
Posts: 2
Joined: Thu Aug 23, 2007 9:24 am


Simply Build It

Postby htg engineer » Thu Aug 23, 2007 3:58 pm

Could be a few different problems, does the central heating demand light come on ? ( a (LED) light on the boiler) if it does then the room thermostat is calling for heat and the problem is with the boiler.

If the demand light to not come on, then its possible the room thermostat is faulty.

The easiest way to check this is to does the room thermostat click when turned up ? if so it's probably ok.

If it does not click, you need a new stat - temporarily you can link out the room thermostat either at the boiler or at the thermostat,


The boiler instructions will show where the room thermostat is connected(normally a terminal blcok next to the PCB). Disconnect these two wires and form a link with a small bit of wire and connect to where the stat should be.

Or take front of the room stat and link the mains LIVE IN to the SWITCH LIVE

if all ok with thermostat etc. then's there's probably a fault on the PCB

hope this helps,
htg engineer
Rank: Project Manager
Posts: 3256
Joined: Tue May 22, 2007 5:22 pm

Postby meongroup » Fri Aug 24, 2007 4:53 pm

Given the situation described, before engaing in a massively expensive repair cycle, consider the simple options first.

Is the pump actually running. If it is located low in the system it is possible that a collection of debris has settled in the pump and stopped it turning. Some pumps have a screwdriver slot in the end of the shaft, you may have to pull off a snap on cover to see it. If there is one try turning the shaft witha screwdriver. This should start the pump turning.

Next, if that doesnt work, check that any changeover valve - if you have a fully pumped system, is actually changing over when you demand heat. there will be a lever on the side with three positions. This lever moves to divert hot water from Water only/ Heat only / Both. Of course if you have a gravity fed hot water system the valve will not be there, and I would put my money on the pump. If it doesnt have a slot in the shaft try tapping it hard with a block of wood - not a steel hammer.
Rank: Labourer
Progress to next rank:
Posts: 1
Joined: Fri Aug 24, 2007 4:43 pm

Postby SidewaysMatt » Fri Aug 24, 2007 6:36 pm

Yes the room thermostat does click, but no LED comes on on the boiler panel.

For info, the boiler model is Greenstar R28 HE if this helps?
Rank: Labourer
Progress to next rank:
Posts: 2
Joined: Thu Aug 23, 2007 9:24 am

Display posts from previous
Sort by
Order by

  • DIY How to Project Guides
  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!

  • Related Topics