Another pump continuously running...

[SgtFoley]

Hi guys

hoping for some advice from the experts before I call someone in.

S-plan system, has been working ok for a few years. Grundfos UPS2 Pump gets power via the boiler (Vaillant EcoTec+ 418... about 6 years old).

The problem: twice now, the pump got stuck on running continuously. It's not the usual pump overrun. The pump symbol on the boiler screen is off (normally on during over-run). No heating/water demand... just keeps going.

This happened previously a month ago. I suspected (from reading forums) a PCB fault, but after repowering the system (after a few hours), it went back to working and worked fine till now.

Is this enough to eliminate the PCB as a possible issue? Could it be a pump fault?
Anything I could check?

Switching off/on after half an hour didn't fix it this time (pump comes on immediately as I repower).

thanks!

 

[SgtFoley]

Bit more info...

When the boiler calls for the pump to come on (i.e. when the pump symbol comes on, following heat demand), I hear a click coming from the boiler/PCB.
I assume this is the relay doing what it is supposed to... but note the pump was already running due to the fault... (would it click if it was stuck on close?).

When the pump symbol on the boiler goes off (after the overrun), there is no click.
Should the relay click when it re-opens?

thx in advance!
S

 

[Gasguru]

The pump can't run without the boiler energizing it so it sounds like the boiler pcb relay is sticking on.
What's the exact Ecotec model? The earlier models are completely different to the later models...You might find the data plate under the boiler.

 

[SgtFoley]

Thank you GasGuru
Ecotec plus 418, VU GB 186/2-O H, Condensing boiler.
(hopefully that's what you mean!)
The PCB is marked 0020080512

I found a forum entry (elsewhere) suggesting the fault could be with one of the motorised valves (providing power when they shouldn't)? I can't quite understand the logic... but may be worth checking?

 

[Gasguru]

The earlier 2006-2015 model version then...
The pump should be wired to the boiler green 3 pin pcb connector and is therefore under the boiler control.
Swing down the controls panel and check the pcb...
Pull up the status codes when the pump is running and see what it says.

If a motorised valve was problematic then you'd find the boiler firing up.
On your system when there is a demand from either the heating or hot water the zone valves open, once open a microswitch inside the actuator operates sending Live to pin 4 at the boiler pcb connector
to tell the boiler to fire up, the pcb then energises the pump (and controls the overun etc)

 

[SgtFoley]

Yes, I think the valves are fine. As you said the boiler doesn't fire... Before your message I tried disconnecting the orange valve wires and the pump kept going.

Status was S30 which I think is "no heating demand". No rad or pump symbol on screen so this makes sense. Yet the pump was running.

Now, as I gave up this evening, the blasted thing started working properly again (similar to what happened a month ago).
This time I paid attention and I hear a click (from the boiler PCB area) when the pump symbol comes on and then another click when the pump symbol goes off.
I'm positive there was no click when the pump symbol went off earlier today (and the pump kept running).

So I'm thinking an intermittently faulty relay on the PCB? (The switch that controls the pump somehow sticks closed?).
Or am I off track?
I read somewhere relays never fail...

I appreciate your help, thank you!

 

[Gasguru]

Relays often fail on boilers and especially if you're unlucky to have a Grundfos pump from a dodgy batch several years ago (the first generation high efficiency model)...the inrush current wasn't sufficiently limited when they powered up and the result was burned out relays.
What pump model is it?
The pump relay on that Vaillant model is next to the large capacitor...sounds like the contacts are sticking on, you should here it click each time it is turned on/off.
If the software sets the pump on it should show the appropriate status code.

 

[SgtFoley]

Grundfos ups2 pH 50-60 (on fixed speed 2).
I had lots of trouble over the years (I'm on the second pump in 6 years). System was originally installed without bypass loop; after that was fixed I tried to mimic zoning with smart rad valves but had lots of flow issues. Then the ABV broke... Overall I suspect the pump has had to work harder than most, so maybe the relay failure is less surprising.

Presumably faulty relay means full PCB replacement or should I be able to replace the part?

 

[Gasguru]

When the UPS2 first came out around 2014 (AFAIR) it pulled a very high inrush current when powered up. After many boiler pcbs/timeclocks etc were damaged Grundfos then issued a "suppressor" lead as a workround.
I suspect it just had an NTC to limit the current. Rumours are that heads rolled at Grundfos.

The lead looked like this... https://phc.parts/product/pump-heads-spares-102952/OBSOLETESuppress-PE2480/PE2480

I don't know when they resolved the issue and modified the pumps. I would talk to Grundfos and check with your pumps serial no.
AFAIR some boiler owners managed to get Grundfos to recompense for the damaged pcbs etc.
Obviously if you've still got a UPS2 without the extra lead or it's not a later batch (without the design fault) you're going to damage the new pcb.

Recon boards are available from CET Ltd if you go down that route (mention the pump relay issue) rather than the extortionate new price.

 

[Harry Bloomfield]

Grundfos ups2 pH 50-60 (on fixed speed 2).
I had lots of trouble over the years (I'm on the second pump in 6 years). System was originally installed without bypass loop; after that was fixed I tried to mimic zoning with smart rad valves but had lots of flow issues. Then the ABV broke... Overall I suspect the pump has had to work harder than most, so maybe the relay failure is less surprising.

Presumably faulty relay means full PCB replacement or should I be able to replace the part?

You could perhaps solve it cheaply by fitting an external to the boiler, more robust relay with a 240v AC coil, operated by the relay on the PCB. If a new PCB is fitted, the same could happen again. The lighter loaded PCB relay, will be less inclined to weld itself up.

 

[Gasguru]

AFAIK the later standalone Grundfos pumps have a PTC to limit inrush current through the bulk capacitor and it's shorted out by a relay shortly after charging..the boiler integral pump models stick with the cheaper NTC option as the pump's energised 24/7 albeit in standby when no heat is demanded.

 

[SgtFoley]

Thanks for the info about the pump issue.

Checked the serial number with Grundfos; they confirm the age of the pump is from the period of the fault (8 years old... I had it for 3 or 4).
But they say if it worked fine until now it can't be due to the 'current inrush' issue.

Does this make sense or are they fobbing me off?
I don't understand the pump design fault enough to know if I could push for a claim... or indeed if I need to change it before sorting out the PCB.

 

[Gasguru]

They're fobbing you off...if they've admitted it's from the batch without the current limiting then there's obviously going to be extra wear and tear on the relay contact set.
They can argue that the pcb relay has lasted a long time and failure is now to be expected due to age regardless of their dodgy pump but I wouldn't countenance that...pump relays can be long lasting.
There's no point in replacing the pcb without the pump unless Vaillant have upgraded their relays ie. they are using contacts with a more durable coating eg. silver tin oxide ...and who knows.
Perhaps Grundfos can send you the suppressor lead to enable you to keep the pump for now.

All modern power supply designs where 240 AC mains is required to be converted to DC (and modern pumps operate at around 325V DC) have a large electrolyitic capacitor and when the pump is first energised this capacitor initially (for a milliseconds) represents a dead short across the mains resulting in a large current flow. If this current is not limited then damage will occur to boiler pcb relays etc. Various schemes are used to mitigate this large inrush current...but it would appear that Grundfos failed to limit the current sufficiently.

 

[Agile]

Most PCB type relays make a click when they are first powered but little noise when power is removed and they open.

I seem to vaguely remember that Grundfos did not give the modified pump lead away free and charged for it.

The most common cause of relays sticking on, is the contacts becoming welded together. This is often caused by closing to a high inrush current. Usually avoided by a suitably specified NTC resistor.

Changing a relay on a PCB is simple enough for anyone experienced in electronics but few would recommend doing that to a DIYer. After doing any work on a boiler gas combustion measurements should be made to ensure correct and safe operation.

 

[Harry Bloomfield]

They're fobbing you off...if they've admitted it's from the batch without the current limiting then there's obviously going to be extra wear and tear on the relay contact set.
They can argue that the pcb relay has lasted a long time and failure is now to be expected due to age regardless of their dodgy pump but I wouldn't countenance that...pump relays can be long lasting.

I agree and it needs to be resolved quickly before your onboard relay is damaged beyond repair and you have to fork out for a new PCB.

The very least Grunfos could do, is send you out the the modification kit, if there is one - I doubt it is anything more than Agile suggested, an NTC to limit the inrush, which cost just a few pence each. It's a simple small component, with only two pins, which needs to be connected in series with the live supply to the pump.

You might even be able to buy the NTC yourself and fit it, if someone can suggest the correct spec for it.