Central heating pump problem

Section62

Upzeecreek said:

If it's a wiring problem, would the fault happen every time rather than intermittently.

It depends.  A heating control system is effectively a logic machine.  There's a collection of switches and sensors using time and temperature to decide whether the boiler should be firing and where the heated water needs to be sent.

Think of it like a much simpler version of the Enigma machine.

Each combination of 'switch' settings gives a different overall system state.  If one combination of 'switches' (aka one 'state') produces a fault condition then the fault will only happen when that particular state occurs.

A control circuit wiring problem can create an 'error of logic' fault - in other words the system will operate consistently, but not in the way you want/expect it to.  The fault can appear to be random and intermittent because there may only be one state (out of many) where it occurs. A problem like that is difficult to diagnose because it means methodically working through all the combinations to find those where the fault can be reproduced, then figuring out the common factor(s).  Also that kind of fault is very different to component failures (like a sticky microswitch) where the occurrence can be far more random.

I'm not saying that is definitely what is wrong in your case - but it would be high on my list of suspicions given you've got three zone valves which is a level of complexity a lot of heating technicians won't deal with on a regular basis.

Upzeecreek said:

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.

You mentioned 'programmers' yesterday - does that (and your comment above) mean there is a programmable room thermostat for each zone?  And if so, how is the hot water cylinder heating controlled?

Upzeecreek

Yes ,there are 2 zones plus hot water. Hot water and down stairs are on one programmer and upstairs zone is controlled by a programmer upstairs ( wireless) 
I can see the fault happening when downstairs heating turning off ( nothing else on) and when upstairs zone is turning off( again nothing else on) 
They are both danfoss programmers and I'm thinking they may both be faulty? 
The fault never occurs when just got water on. 

knightstyle

I haven't read the whole thread but a similar intermittent problem we had years ago was a flow switch sticking. would usually work with a sharp tap to the pipe. 

ispookie666

Upzeecreek said:

Yes ,there are 2 zones plus hot water. Hot water and down stairs are on one programmer and upstairs zone is controlled by a programmer upstairs ( wireless) 
I can see the fault happening when downstairs heating turning off ( nothing else on) and when upstairs zone is turning off( again nothing else on) 
They are both danfoss programmers and I'm thinking they may both be faulty? 
The fault never occurs when just got water on. 

Are you saying, the fault can be recreated by following a specific sequence?

Upzeecreek

It seems if I set the required temp 1/2 degree above actual temp of room, then it causes the boiler to turn on/ off  several times in succession as it seems it ( thermostat? ) can't decide if it's up to temp or not. That increases the likelihood of the fault occuring.NB that technique doesn't always work!  

Bendy_House

Upzeecreek said:

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. 

So 'C' would seem to just indicate that the boiler knows it's being 'asked' to provide CH, but it's the boiler wot then decides when to turn the burner on and off in order to provide this.

When the burner is actually on, there's a 'C' showing and a blue background and burner symbol as well, and when the boiler reckons it's provided enough heat for the 'flow' demand, but the called-for temp has only just been reached (or perhaps hasn't quite been so), the burner goes off for a bit but the 'C' remains to indicate "I'm still running, and still on the case...".

Only when the actual room temp has firmly been reached, or when the programmer's timer says 'offski', does the boiler get told to 'shut off now', and the 'C' goes away - and the pump goes off.

In which case, I think this behaviour could be normal?

What make of programmer is this? Is it an 'Opentherm' type, for example? These, as I understand it, have a more sophisticated type of 2-way(?) communication between the boiler and 'stat in that the boiler isn't just told to "come on until it's 20oC' and then go off until it's 19.5oC. Then come back on again..." like most room stats do, but more like "OOokkaaay - we are nearly at the asked-for 20oC, so start to back off there. Good. Ok, ease off a bit more... Nice! Right. We are almost at 20oC here, so you need to throttle back a teeny bit more. What? You cannot without actually turning off your burner for a bit? Ok, that's fine - turn off your burner, but keep the pump running - oh, and can you keep displaying 'C' as well, please, so that Upzee knows what you are doing? Cheers."

In which case, this is normal pump control by a more complex boiler/prog combination.

Possibly.

Try emailing the Prog and boiler manufacturers describing your observations?

Bendy_House

Mind you, if the programmer definitely goes 'off' - as in fully off at a set time - then the pump should stop pretty soon after this, once the boiler water has been dispersed - ie the 'pump overrun' status is over, surely only a few minutes?

Make and model of Prog?

Section62

Bendy_House said:

Mind you, if the programmer definitely goes 'off' - as in fully off at a set time - then the pump should stop pretty soon after this, once the boiler water has been dispersed - ie the 'pump overrun' status is over, surely only a few minutes?

Yes, which is why (in the absence of there being a faulty component) I'd suspect some kind of wiring fault so the pump and/or boiler is being energised via an unexpected route and bypassing the usual time/temperature controls.

As an example (not saying this is what the OP has) if there was an old (i.e. should be disused) room thermostat which acted as a 'short' from the mains live to the pump the pump could run semi-independently of the rest of the heating control system.

When you add to the mix that some controls have both NO and NC terminals, some room stats had/have compensating resistors, and the labelling of terminals isn't always consistent, there's plenty of scope for someone who wasn't really sure what they were doing wiring up a heating control system which works most of the time, but can throw up apparently random 'faults'.

If all the parts are believed to be working as they should, the sensible place to go next is to trace out the whole system - accounting for every wire and terminal - to make sure everything is where it should be, and as importantly, that there's nothing there that shouldn't be.  A job like that is probably beyond the average low-cost boiler servicing technician, it would need input from someone methodical and with the expertise to understand exactly what is happening.

Upzeecreek

Thanks for all the comments. 
Just to clarify, under normal operation the c on the boiler only appears when there is a call for heat and then when the boiler is lit. When the room stat is up to temp and the boiler isn't required it goes into standby and there is a 0 in the display and pump shut down in airing cupboard. Over run on boiler for 2 mins. 
When it's playing up, instead of going into standby with a 0 , it displays C and pump continues to run in airing cupboard. It still does the over run for 2 mins and goes quiet with C being displayed.
It would stay like this with the pump running for hours if I don't switch off at the wall.
 Turning it back on after an hour will sometimes clear the fault and return the status to 0 on the boiler. 
Programmers are danfoss  62057 ( mains wired)
and danfoss 40704 ( wireless with new batteries) 
Thanks

Another_Level

Upzeecreek said:

Just looking for some advice on a central heating pump problem. 
When all the timers are set to off the boiler pump continues to run ( for hours ). On the info panel on boiler it is saying "c" but not actually firing.( Although I noticed last night it did fire up for about 20 secs and then stop) 

During the recent pump continuous running events has the boiler actually fired up D emand neon illuminated. boiler flow pipe hot etc.

The fault is either inside the boiler or the bespoke system its installed on. Elimination is required 

As mentioned by section62 there is an electrical switch live demand from somewhere, really needs a clued up service tech to locate the fault 

Has any visiting service tech (they have a hotline) phoned ideal technical. Some boilers have unusual faults,which the manufacture knows about.

The problem is fixable 

Can you use a multimeter ?

Edited to add. Have any internet,wifi, bluetooth items been added to the original installation. Or any diy work