DIY Doctor

Main navigation

How to stop cycling and reduce dom water temp

Postby ericmark » Sat Jan 12, 2008 2:17 am

My father has a central heating system where a thermo siphon hot coil heats the domestic hot water and central heating is pumped. There is no thermostat on the cistern. There are no motorised valves. There is a programmer and a room thermostat. The boiler keeps cycling which since the pipes are under floor boards and the bed rooms get too hot. The hot water also becomes too hot. There seems to be two ways forward. Method one is just fit a cistern thermostat common to Boiler normally closed to pump and normally open to programmer hot water output. This will stop boiler cycling it would only run if central heating or hot water was required. But when central heating is running water will still heat in cistern but since pump should push most of the water around the central heating it may be very little? It will require one three and earth cable routing. Second is to fit cylinder stat which controls a motorised valve which has a change over switch incorporated that switch then controlling boiler Orange to boiler, Brown and grey to cylinder stat and White to pump. In both cases room stat also connects to pump. The latter needs 4 wires plus earth as it will require a neutral and extra cost of valve plus plumbing will be required to fit valve. I am sure I am not the first to be faced with this problem and wonder if the first method has ever been tried and how well it worked. Second method connects the valve in a way I have never seen in any books again has anyone tried it and how did it work.
I have built circuit in multisim and tested and shown to be electrically sound but no way that I have to simulate water flow.

Thanks Eric

PS I am sticking same post in plumbing and Electrics as it involves both trades.


Simply Build It

Postby htg engineer » Sat Jan 12, 2008 1:24 pm


turn boiler stat down when hot water only selected, this will stop the water getting too hot.


convert to a fully pumped system, where a cylinder stat can be fitted. Alot of work and hassle, depends on the age of the system whether it is worth doing.

Install a combi boiler, water is heated when needed.
htg engineer
Rank: Project Manager
Posts: 3256
Joined: Tue May 22, 2007 5:22 pm

Postby ericmark » Sun Jan 13, 2008 1:22 pm

I have found the answer there is a standard "C" plan which although it uses one more wire than the one I had designed is an industrial standard so any one working on it in the future will not have any problems following what has been done. I will run twin and earth plus three and earth between airing cupboard with thermostat and two port 5 wire valve and kitchen where everything else is terminated is there a standard for cable colours between the two if so I want to follow it. I will of course use brown sleeves on all wires except for neutral. One option is to fit valve in kitchen need to boiler and use radio control thermostat but they are a bit expensive. I am not sure if this is considered new circuit Part P is free because they are disabled I expect the same with Part L not sure if I need to submit installation certs or not and not a clue what paperwork required for Part L. Any advice. I do have the meters required to inspect and test and the qualification's required for Part P but not registered.

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