S Plan heating system, heating coming on with hot water

[Sandeep89]

Hi Guys,

Had a question about a S plan system. When customer turns on a hot water tap the boiler gets demand for heating as well and radiators heat up, the heating radiator sign (Vaillant Boiler) flashes on the boiler display screen.

Customer has said it has been like this for a year.

I have checked the 3 port valve and the spindle is totally free, when there is demand for heating with hot water tap on and also just when the heating is running on it's own.

Would I be looking at a faulty motorised valve head?

 

[Chuck]

Yes, that's a likely possibility. I'd check the voltages at the valve head are correctly reflecting calls for heat as the first step.

If you are not familiar with using a multimeter to diagnose this sort of fault get a sparks to help / teach you how it's done correctly and safely. (Or take a training course of some sort.)

 

[ShaunCorbs]

Combi boiler ?

 

[Deleted member 120897]

The boiler would only fire up once a demand has been requested, so either it’s a Combi, or you have a different fault. Check the 24v link hasn’t been left in.

 

[Sandeep89]

Combi boiler ?

Hi ShaunCorbs,

It is a system boiler, customer has a hot water tank upstairs in the airing cupboard and there is one Honeywell 3 port zone valve.

 

[ShaunCorbs]

It won’t be firing on hot water / after it’s used unless it’s constantly on hw or wired wrong also 3 port on a unvented is a nono

 

[Sandeep89]

It won’t be firing on hot water / after it’s used unless it’s constantly on hw or wired wrong also 3 port on a unvented is a nono

Landlord is adamant it was all ok whilst they were living in the house however tenants said past year since they moved in issue has been there.

With the CH off at the programmer, with a hot water tap run CH demand still kicks in at the boiler and burner comes on.

I will be going back to investigate further.

 

[ShaunCorbs]

You sure it’s not a combi that’s been used as a sys / heat only as you would need to run a fair bit of hw off before it calls for reheat if fed via cylinder?

 

[John.g]

Does the CH come on immediately on opening a HW tap even with the cylinder stat satisfied?.

 

[Deleted member 120897]

So it’s a Y plan, not an S plan. Just go armed with a multimeter and check voltages.

 

[Murdoch]

Y plan and not a combi surely

sounds like something is rather amiss

 

[Chuck]

I'd expect there to be a programmer ('time switch') for the hot water. Connected in series with the tank thermostat and set so the tank is reheated for a couple of hours a day in the night.

The behaviour described in post #1 suggests that this programmer is missing or has been set to 'always on'.

 

[Sandeep89]

Hi Guys,

Was away on leave. Yes system is a Y plan with one 3 port valve. So while I have been away customer got another engineer out who replaced the 3 port valve and issue still persists.

I have come back and there is a Drayton Lifestyle programmer. When the hot water is turned is selected to 'on' on the programmer and heating off at the programmer the heating kicks in at the boiler.

I checked the new valve and again the arm/lever is totally free however if I remove the motorised head from the body the arm/lever moves back and I can then put it into manual. Put with the valve connected back to the body the arm is totally free.

With the hot water on at the programmer and heating off, if I turn the cylinder stat off the heating turns off at the boiler, but when cylinder stat is turned back up heating kicks back in again at boiler.

 

[Sandeep89]

This is the Drayton Lifestyle programmer wiring.

 

[Deleted member 120897]

Sounds like a wiring fault, need to fault find at the wiring center. Would double check the hot water off is actually hot water off.