Y Plan / Mid Position Valve - Odd Boiler Behaviour

[lilman]

Hi all

Looked at a basic wiring set-up with programmer (dual channel), mid position valve, cylinder stat (no room stat) and Keston boiler. Heating engineer stumped so I had a look. If CH is selected at programmer the boiler fires as it should; when CH is set to off - the boiler remains on? Measured 89V at switched live. I know Honeywell valves 'leak' a bit of voltage - not normally enough for this to happen. Heating engineer had replaced the valve twice. What's occurring?

 

[bryanh]

All new boilers control their selves for cooling reasons assuming its not that then is the cylinder Stat calling for heat ?

 

[lilman]

Took the cylinder stat out of circuit. It's not the boiler overrun either. I think on Viessmann boilers there is a little gizmo (capacitor?) across the switch live terminal to stop this occurring?

 

[Riggy]

What make/model is the programmer?

It sounds like it may be one with an electronic rather than relay output, and there's not sufficient load from the boiler control to pull the voltage down. Daft as it sounds, try connecting a 60W lamp across (i.e. in parallel with) the boiler fire signal. That will prove me right or (as usual) wrong.

 

[Steve3948]

Hi all

Looked at a basic wiring set-up with programmer (dual channel), mid position valve, cylinder stat (no room stat) and Keston boiler. Heating engineer stumped so I had a look. If CH is selected at programmer the boiler fires as it should; when CH is set to off - the boiler remains on? Measured 89V at switched live. I know Honeywell valves 'leak' a bit of voltage - not normally enough for this to happen. Heating engineer had replaced the valve twice. What's occurring?

When you say 89V at switched live, was this at the terminal or with the switched live (trigger) out of the connection ???

Could be the opposite of what your thinking.

 

[Marvo]

How did you measure the 89V? Was it between the switched live and earth or to neutral? Were you using a digital tester with a ridiculously high input resistance? Unless it's a solid state switch, 89V on a switched live sounds odd, it should either be 230v or zero wrt ground or neutral. It sounds like your tester is oversensitive and is giving a reading of a capacitively induced signal. The only other reason for this type of reading can think of is maybe some condensation in the switch.

 

[batty]

Y plans are like capping the devils work. S plans any day a lot less problems and fewer breakdowns. I have a Y plan in my house its gone wrong more times than I can remember.

 

[lilman]

Quick update - visited premises again today. Heating engineer changed valve for another Honeywell 3 way. Same problem. All connections to boiler removed. Cylinder stat removed. No room stat. Hot water on 230V at sw live out. Hot water off 0V at sw live. Heating on 230V. Heating off 109V. Did notice that the valve seems to stop momentarlly at 109V on the way to 230V when the heating is switched. I'm stumped. Definately not the boiler. Wiring centre is all good. Tried replacement programmer. Only thing it could be is a duff batch of Honeywell valves? Engineer is gonna try it with a Drayton valve. I'll let you know the outcome.

 

[Steve3948]

You have boiler switch live connected to Orange and how are you connected with the others.

 

[steptoe]

Y plans are like capping the devils work. S plans any day a lot less problems and fewer breakdowns. I have a Y plan in my house its gone wrong more times than I can remember.

you need to get a spark in mate.

 

[Steve3948]

Hot Water Off should have output and be connected to the Grey of the 3 Way Valve and the satisfied connection. of the cylinder stat terminal 2.

Heating through Stat to White on 3 Way Valve.

Hot Water on through cylinder stat common through to calling terminal 1 with Orange of 3 Way Valve, boiler and pump.

 

[steptoe]

do you want a wiring diagram?

 

[lilman]

I understand how to wire a system - anyone else had this errant voltage on white wire when heating switches off. Its obviously enough to keep the boiler running!

 

[Steve3948]

I understand how to wire a system - anyone else had this errant voltage on white wire when heating switches off. Its obviously enough to keep the boiler running!

It's a micro switch array inside the valve head, make or break and that's it, the voltage comes from the programmer through the stats opens/closes valve motor in turn switching auxiliary contacts in valve to then energise boiler and pump.

In your post you said you had nothing on Hot Water off, a Y Plan needs an output from programmer when hot water is off to work correctly.

Is it a system boiler, built in programmer, pump etc.

 

[NozSpark]

In this situation I would remake all the terminations ensuring that it was wired correctly

 

[lilman]

Left it to the heating engineer - he can work it out! Everything is wired correctly - I'm stumped. I'll let you know the outcome.

 

[PC Electrics]

You should check you have a "hot water off" signal correctly wired and working. You've been asked twice (above) about this and not answered, which leads me to suspect you don't understand the significance of this signal in a Y plan.

 

[Sidewinder]

By "heating engineer", I think you mean plumber mate!

 

[PC Electrics]

For the right price I'll come and sort it out. I can do Y plans in my sleep!

 

[Steve3948]

For the right price I'll come and sort it out. I can do Y plans in my sleep!

Same, did 700 over a period of 4 years, every Thursday and Friday.