Upgrading simple CH system

[Keefiedee]

Hi,

I have an oil fired boiler with a very traditional old-fashioned system - pumped central heating, indirect hot water tank and gravity hot water. It is controlled by an old Randall 103 which just switches the whole system on or off, a room thermostat switching the CH pump on and off, and a very antique tank thermostat (calibrated in fahrenheit) - I'm not really at all sure what that controls. When the room thermostat isn't calling for heat the boiler still seems to cycle rather a lot - presumably keeping the HW up to temperature. I feel it might improve things considerably, at moderate cost, to fit a pump to the HW side, controlled by the tank thermostat. But I also suspect the tank thermostat is misbehaving - would that cause cycling?

Any help and advice would be very gratefully received.

TIA

Keith

 

[gas4you]

The cycling is caused by the HW being on a gravity circuit so the boiler will want to keep this at the temp set on the boiler stat.

As there is nothing on the system to tell the boiler that everything is up to temperature and not to fire, it will keep firing just to keep its self hot, wasting loads of your oil Your room stat will just control the pump.

Modern systems, fully pumped are wired so that when the room stat and cylinder stat are satisfied the boiler is electrically isolated and therefore cannot fire unless a stat tells it something needs heat.

You will see this refered to as a boiler interlock.

To do a proper job you will need to convert your system to fully pumped with new controls including a full programmer.

 

[Keefiedee]

Yes, thanks, I guessed that was what my problem was. I'm just not too sure how to move forward, and where to find wiring diagrams etc.

The layout of the pipework of the boiler is such that I feel it would be easier for me to pump the hot water circuit by fitting pump in the hot water pipework rather than change all the pipework and install valve(s). Is there any reason I shouldn't do that?

Presumably the tank thermostat would then control the hot water pump? Can you point me where there is a wiring diagram that would give the result you describe?

Many thanks

Keith