RANDALL 4033 mechanical timer Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[trevor123]

hi, i have the above timer on my gas central heating system, i would like to change it to a 5/2 or 7 day digital timer with independant water and heating timing? it has 3 wires going into the bottom of it, 1 goes to a fused switch which goes to another fused switch which is the immersion, the other 2 wires go to a box which goes to supplies the motorised valve, cylinder thermostat and the pump. is this a simple exchange or do i need to get someone in? im a fairly competent diy'er. i would also like to add a thermostat somewhere as we dont have 1, would this be straightforward too, the boiler is downstairs and the hot cylinder is upstairs if this helps? regards trevor
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[ericmark]

The wiring on the older pre-combi central heating and hot water systems tend to follow one of the honeywell plans. C, S, Y etc. To understand what you have we need to work out which system it is using. You may be able to find the part number of your valve and find out what type there is the two port and three port and with three port we have mid position and change over although the latter are rare.
I can't understand why there should be two fused switched units unless one for central heating boiler and other for immersion heater the latter is normally independent to central heating.
For the domestic electrician the central heating can be the most complicated part of the house wiring.
I don't know your timer but most do basically same job but some systems will not allow you to have central heating without hot water knowing if it is that type will help. Not sure why anyone would want to turn off hot water and simply turning the timer on constant and fitting a new thermostat with timer built in is relatively easy. Neutral no longer used so only two wires com and NO normally open the NC is not used. Then heating does not switch off it just changes temp a lot better idea.

[trevor123]

hi ericmark, the first fused switch is switched and the latter being the immersion is switched off at present. the timer has a seperate on/off?constant for heating and water. the reason i ask is because i would like hot water at times when i dont want heating, ie from 4pm so tha the water is hot for when i arrive home at 6pm for a bath. in the summer this will not be a problem although in the winter the house would be cooking and i'd have to alter all thermo valves everyday to suit.
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[ericmark]

I would go for the simple just replace the thermostat for one with timer built in then set central heating on old clock to on all the time and use the old one to control hot water and new thermostat/Timer the central heating. Not really worth the problems involved in complete change.

[trevor123]

thanks ericmark, do you have any suggested makes and model numbers for a new timer/thermostat please? would be wired direct to the boiler or to the control boxes upstairs in the cupboard with the tank?
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Suzuki RV90