Central heating pump problem

Upzeecreek

So, further to update....no problem has occured with the boiler shutting down over the summer with just the water being on. But now we are having heating on,the problem has started again. 
The issue now is that we have the problem with both the upstairs zone and down stairs zone independently. I can't believe it is a zone valve causing this problem now. Particularly as they have been replaced.
After observing the programmers, they seem to be behaving oddly ( both danfoss). They seem to be turning the heating off when it's not up to temp and I'm hearing rapid clicking of  it turning the boiler on and off...( unfortunately it's an intermittent problem!) 
Just gathering more evidence before I call in BG.

ispookie666

A wild guess - the pump is on its way out.  

Upzeecreek

Pump replaced 2 months ago! 

Bendy_House

Annoying, eh?!

Looking over the thread, it still isn't clear whether the pump is controlled by the programmer/motorised valves, or by the boiler. I think this will almost certainly indicate where the fault is.

It works like this: The programmer says 'Turn CH zone on'. If you have a separate room stat, then this gets an 'on' signal from the programmer. If the room stat also 'calls for heat', this sends a signal to the motorised valve. The valve goes 'whirrrr-click', and this sends a signal to the boiler (and pump) to come on.

Ok, two ways the pump can be wired. The more basic way is that it's wired in parallel with the boiler; inside that wiring centre, the 'orange' wire from the motorised valve (the one that gives out that last 'on' signal) is connected to the boiler 'switching' wire, and also to the pump 'live'. So, when the orange goes 'on' so does the boiler and the pump - individually, but at the same time. With this setup, when the motorised valve closes (ie when the room stat and/or the programmer says 'offski') then the boiler and pump are immediately turned off.

The more complex way (which I assume you have) is that the orange wire only goes to the boiler to tell it when it should come on. The boiler then controls the pump so that it tells the pump when to come on, and - when needed - to stay on until all the hot water has been dispelled (pump 'overrun').

For the 'basic' scenario, if there is a fault in a motorised valve which is making it keep that orange wire 'live' even after the stat/programmer has gone 'off', then this should be obvious since the boiler should also stay on when it shouldn't. So, it shouldn't just be the pump that's running, but the boiler should be trying to run as well. Is that the case? (Bearing in mind that if the motorised valve has physically closed but is still sending an 'orange' 'on' signal, the boiler won't be able to run properly as the water will have nowhere to go, so the boiler will keep shutting down due to 'overheating').

So, when the pump runs when it shouldn't, does the boiler look as tho' it's trying to run too?

With the other wiring method - ie the pump is controlled purely by the boiler and not by the prog/stat/motorised valve - then you can most likely point to a fault in the boiler itself, most likely to do with the PCB. This could be as simple as a sticking relay. It could also be due to other features - such as frost stat, pump overrun, pump 'exercise' etc - not working properly, so causing the pump to run when it shouldn't be.

ispookie666

I hope you get to the bottom of this. 
When we moved house in Dec last year, it took me a long time to sort out our CH (oil). It is an S plan system, but all the wires had live feed (including 3 wires in the thermostat) and the heating was all over the place. 
After spending a long time, I traced it back to incorrect wiring on Programmer (some cowboy heating "engineer" has swapped the L and N). 
Anyway, swapped the 40yr old boiler and circulation pump last month. 😊

My only suggestion if going down this route of checking every connection, use your smartphone to take as many pictures of wiring connections as possible, once you untangle the wires, all of them look the same!!!! And a good multimeter

Bendy_House

I take it your fault was a permanent one, iSpook? Upzee's is made more tricky by seemingly being intermittent.

Upzeecreek

Under normal operation, when the room thermostat is up to temp, I hear the programmer click  and the red light goes off. The instant the light goes off, the pump and in airing cupboard shuts off ( all valves appear to be closed) and the boiler after a fews secs powers down and then  it shows 0 is the display. There is an over run for 2 mins before boiler is quiet. 

When I know there is going to be a fault, the same red light goes off and there is a click from programmer but pump continues to run in airing cupboard and I can hear water circulating in airing cupboard. Again, after a few sec boiler powers down but rather than 0 in display there is a c in the display.  The boiler does not fire up until another call for heat.
I have had a motorised valve fail and in this scenario the zone valve remained open and the boiler continued to be fired up and running. 

Bendy_House

On the assumption that the boiler controls the pump in your setup, I think the boiler itself is the most likely contender for having an issue.

'c' means there's a call for heat - the boiler should be on? Does 'c' show under normal running circumstances? And yet, when this fault is apparent, 'c' still shows but the boiler itself doesn't run, just the pump?

Anyhoo, you need someone oot.

Section62

Upzeecreek said:

Under normal operation, when the room thermostat is up to temp, I hear the programmer click  and the red light goes off. The instant the light goes off, the pump and in airing cupboard shuts off ( all valves appear to be closed) and the boiler after a fews secs powers down and then  it shows 0 is the display. There is an over run for 2 mins before boiler is quiet. 

Can you confirm the red light is on the programmer (on the central heating side, if applicable)?  Or is this red light somewhere else?

Upzeecreek said:

When I know there is going to be a fault, the same red light goes off and there is a click from programmer but pump continues to run in airing cupboard and I can hear water circulating in airing cupboard. Again, after a few sec boiler powers down but rather than 0 in display there is a c in the display.

If the click is from the programmer relay - and assuming the relay isn't faulty - the fact the pump continues to run suggests it is energised from a source bypassing the programmer function.

That suggests either -
1) The programmer relay is faulty and not switching off properly.
2) The pump has been wired up (via the boiler?) in an overrun configuration.

A quick google seems to confirm that the 'C' on the display means the boiler is receiving a call for the central heating.  If that is happening when the central heating programmer is definitely off, then it implies that the central heating has been wired incorrectly.

I think you need to get an electrician with experience of central heating systems to check the whole installation.

The problem with intermittent faults is recreating the fault during testing, so the standard-grade boiler servicing technician is not necessarily going to have the skills to identify the true cause of an intermittent fault.  It really needs going back to first principles, tracing the wiring and see what is connected to what, and that all the connections are to the right terminals and secure.

Alternatively, you could assume it is a faulty programmer and just get that replaced and see if the fault continues or reappears.

Upzeecreek

Sorry, yes red light is on programmer. 
If it's a wiring problem, would the fault happen every time rather than intermittently. 
So just had heating on and display on programmer says room temp is 17⁰ but I have asked it to heat up to 17.5. Boiler fired up initially as normal but  programmer has just clicked off and red light gone off on programmer  dispite the fact it's not reached the 17.5 but boiler now has c on it and not firing. Fault has appeared. 
C is on display when there is a call for heat and when boiler fires there is a blue back ground and burner light displayed.