central heating pump won't switch off

[GeX]

Hi all. Any ideas why my central heating pump won't switch off?

Boiler is a Vaillant Ecotec Plus 418 Condensing boiler, it is controlled by an iflo programmer. There are two electronic valves, and there is a hot water cylinder with stat upstairs.

I know that the boiler is supposed to overun the pump when the boiler shuts off. This is meant to be for 5 minutes.

However, I noticed last night that the pump was still going long after the heating had been turned off. I thought nothing of it, and went to bed. The heating or hot water was not set to come on at all overnight.

So this morning I checked it again, and the pump is still on. The rads are cold (as they should be), but the pump is hot. The screen on the boiler was showing approx 70deg. It is pumping water around the hot water cylinder circuit.

If put the heating on, then the valves move as they should and the rads warm as they should. But then once the boiler turns off, the pump keeps running.

The boiler has an information button, which tells you what state it is in when you press it. Overun is S7, and this is displayed for 5 mins after boiler shut down. After 5 mins it displays S0 (no heat required) and the pump just keeps running.

The boiler, programmer, cylinder stat and valves are all around 6 months old. Is there anything simple I can try before getting a plumber out?

(yes, I've tried turning it off and on again )

 

[Drukk]

I had exactly the same problem a few months back. The system I have has auxilary contacts on the hot water and heating shut off valves which control the power to the pump.

The timer powers the valve open which then closes the contacts in the valve head which turns the pump on.

The switch in one of those valves was sticking so I just changed the head unit off the valve.

Don't know your system and I am no heating expert but that was the problem I had.

 

[GeX]

I've tried given the valves a light tap to see if they'd stuck (I can see them both operate though). It didn't help

Luckily this place is rented, but wanted to try and save the landlady the hassle/money.

 

[Mel_P]

My daughter's central heating had this problem and it was the contacts on a small microswitch on the valve which were welded together - so hot water was on constantly. She didn't notice - I noticed that the airing cupboard door was always warm!

 

[GeX]

This has happened again. I 'fixed' it last time by messing around with putting the H/W on, the CH on, messing with the thermostat etc etc.

I have looked through the diagnostic codes, trying to get an idea of why the boiler thinks it needs the pump on.

Both LEDs on the controller are off, the LEDs show when HW or CH is meant to be on.

These are some of the status'

d.4 -> Current temp for warm start sensor (when accessories are fitted) Current storage tank sensor -> -99
d.5 -> Flow temperature target value or return target value when return regulation is set -> 73
d.6 -> Hot water temp target value -> 65
d.8 -> External controls heat demand (terminals 3-4) -> 1, closed, heat requested
d.9 -> Flow target temperature from external analogue regulator to terminal 7-8-9/eBUS -> 90
d.10 -> Status internal heat pump -> 1 = on
d.11 -> Status external heat pump -> 1 = on
d.13 -> Hot water circulation pump -> 0 = off
d.22 -> Hot water demand -> 0 = off
d.35 -> Position of diverter valve -> 0 = off

Any plumbers out there shed some light on this?

 

[Fuzz]

I think you've gone beyond the call of duty in trying to diagnose it yourself.
Just contact the landlord / letting agent and let them sort it out, it is after all, just rented and not your problem.

 

[Mickie]

This has happened again. I 'fixed' it last time by messing around with putting the H/W on, the CH on, messing with the thermostat etc etc.

I have looked through the diagnostic codes, trying to get an idea of why the boiler thinks it needs the pump on.

Both LEDs on the controller are off, the LEDs show when HW or CH is meant to be on.

These are some of the status'

d.4 -> Current temp for warm start sensor (when accessories are fitted) Current storage tank sensor -> -99
d.5 -> Flow temperature target value or return target value when return regulation is set -> 73
d.6 -> Hot water temp target value -> 65
d.8 -> External controls heat demand (terminals 3-4) -> 1, closed, heat requested
d.9 -> Flow target temperature from external analogue regulator to terminal 7-8-9/eBUS -> 90
d.10 -> Status internal heat pump -> 1 = on
d.11 -> Status external heat pump -> 1 = on
d.13 -> Hot water circulation pump -> 0 = off
d.22 -> Hot water demand -> 0 = off
d.35 -> Position of diverter valve -> 0 = off

Any plumbers out there shed some light on this?

stop being a freeloader, get your landlord to pay a plumber to fix it, im sure they'd rather get paid than give out free advice..

 

[St0rmer66]

This has happened again. I 'fixed' it last time by messing around with putting the H/W on, the CH on, messing with the thermostat etc etc.

I have looked through the diagnostic codes, trying to get an idea of why the boiler thinks it needs the pump on.

Both LEDs on the controller are off, the LEDs show when HW or CH is meant to be on.

These are some of the status'

d.4 -> Current temp for warm start sensor (when accessories are fitted) Current storage tank sensor -> -99
d.5 -> Flow temperature target value or return target value when return regulation is set -> 73
d.6 -> Hot water temp target value -> 65
d.8 -> External controls heat demand (terminals 3-4) -> 1, closed, heat requested
d.9 -> Flow target temperature from external analogue regulator to terminal 7-8-9/eBUS -> 90
d.10 -> Status internal heat pump -> 1 = on
d.11 -> Status external heat pump -> 1 = on
d.13 -> Hot water circulation pump -> 0 = off
d.22 -> Hot water demand -> 0 = off
d.35 -> Position of diverter valve -> 0 = off

Any plumbers out there shed some light on this?

Most of those codes are irrelevant to you, they're for different models which just have the same electronics (without all the extra sensors/equipment plugged in). For example d.22 is for a combi-boiler when you run the tap and d.35 is also for the combi (which has a built in diverter valve).

Sounds to me as if the hot water actuator is constantly calling for heat as some other people have mentioned. It can do this regardless of what the timer or thermostat are doing because it has a micro-switch with a permanent live on one end and the demand wire to the boiler on the other! So if the micro-switch is stuck on, even if the valve closes the boiler will still "try" to heat the water (and go round the bypass instead of round the heating or hot water circuit).