Central heating demand also turns on hot water Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[Bobbedi]

Hi all,

Excuse me if I get some of the technical detail/terminology wrong.

Ideal Classic FF280 boiler, vented indirect cylinder, 2 individual 2-port zone valve actuators (one each for CH and HW) - so I'm guessing I've got an S-plan system. Spindles on both CH and HW valve heads are free and not sticking, and valves move freely when turned by hand.

When I say below that the CH/HW is ON, I mean that the boiler controller/heating/water programmer box (not sure what it's called) is set to supply that part of the system. This is the box that controls On/Off/Once/Twice etc.

1. Last week the heating stopped working. I got by temporarily by forcing the HW ON (to force the pump and boiler to operate), then using the manual slide switch on the CH actuator to get heat to the radiators.

2. Yesterday, I replaced the CH actuator and checked the motor moved correctly when CH was demanded (CH ON and room thermostat 30 degrees) before attaching to the valve head.

3. Now it appears that the CH works 'correctly' i.e. with CH ON and thermostat demanding heat, the valve head opens and radiators get warm. However, when the CH is supplying the rads, the HW valve actuator is also ON/Open, even though the HW is OFF. I.e. there should be no call for HW, but it seems that the CH is somehow demanding it?

Very confused, and wondering if there's a wiring issue (which must have always been there - but maybe I've not noticed this before)? Could it be that a wiring problem would make HW turn on when only CH is called for?

Thanks.

[ericmark]

With the old programmer there was an option for C Plan, with C Plan you can't turn off the DHW, so there were often two switch like devices in the programmer, one physically stopped you selecting CH without DHW and the other set it electrically.

Could you have altered the turn buckle or dip switch on the programmer?

[Bobbedi]

Thanks for the reply.

I haven't been inside the programmer, so unless it's been set up incorrectly since installation (20 years ago?), then It's not something I've altered.

Having done a bit more digging, the sequence of events looks like this:

- HW selected OFF on programmer (hence should never come on)
- CH selected ON on programmer (CH now called by room thermostat)
- CH called by turning room thermostat to 30 degrees
- CH zone actuator valve opens
- Pump comes on, then HW zone actuator valve opens

So to my untrained eye, it looks like there's a wiring issue with the pump and/or HW zone valve actuator?

I also had a little look at the wire jungle in the airing cupboard, and there is an un-connected red live wire - it just terminates itself in a terminal block, whilst all other wires have at least one other wire joined to them - does that sound normal?

Thanks again

[ericmark]

My daughters first house had Y Plan, and it went wrong after son-in-law had played in airing cupboard, it turned out the three port valve had failed before they bought the house, and to keep it running the last owners had latched the bleeding lever on the valve, which would mean in summer the radiators would warm up a little when the DHW called for heat, but she had never realised it was happening.

So may be previous heating was C Plan and some one has not changes the dip switch? It is not some thing you look for.

From the programmer it goes to the two thermostats, one for room temperature the other for cylinder temperature and from thermostats to the brown wire on the two port valve, can't see how the valve can open unless brown wire is line. There is also a grey and orange wire to the valve, grey always line and orange goes to boiler and pump, but unlike the three port there is no internal linking between the brown/blue and grey/orange so can't see how a fault in valve would cause it.

Some wiring centres did have relays in them, but never worked on one, so not sure why they had them or what they did.

[Bobbedi]

Called a heating person, who in turn had to call an electrician.

There was a problem in the wiring centre, along with a fused micro-switch on the HW valve head.