Vaillant Ecotec Pro 28, new pump fitted, now boiler won't turn on

Hi guys, my first post here, but I won't lie, I've used this place as a reference point so many times it's been invaluable, so I thought I'd sign up and ask a question I have. I will give as much info as possible so forgive the long read...



Last week the pump on my mom's boiler went, as per the title it's a Vaillant Ecotec Pro 28. I contacted a local parts place who were very helpful, and after I gave them the gas certification number on the boiler, the part came up and I ordered it.

Today, I finished work, collected the part and proceeded to go and change the pump. All went well, no issues during installation, and so after filling the boiler back up I turn on the electrical supply to the boiler. This is where things took a turn.

The green light comes on, the LCD display shows 2 dashes, there's a very faint click within the PCB area, and it then proceeds to shut off (green light goes of and display is blank), all within about 1 second. I have a video of this and can upload to YouTube if it helps.

Now, the thing I've noticed is that the pump removed had a 3 wire multiplug. The new pump has a 5 wire multiplug. The PCB has a socket to receive a 5 wire multiplug. When I was researching prior to choosing a local parts place, I had read about there being 2 different brands (Wilo and Grundfos), and with the latter being an improved pump, my assumption was that this was part of the upgrade, the PCB takes a 5 wire multiplug and I had given the exact number for my boiler to my supplier and they provided the exact pump I needed.

Clearly now, I am fearing the worst that I have potentially blown my PCB by using a pump it can't handle, despite the allowance for the plug it has and my confidence that I was provided the correct part for the exact boiler. And of course doing a search for "5 wires" shows adverts for the pump stating "5 wires only".


I'm going to call my supplier tomorrow for their opinion, but I'd like your input too so I am armed with as much info as possible. Prior to fitting the new pump the boiler did fire up and try to work so all was well apart from the pump being broke. If I now plug the old pump in (despite not being plumbed in) it still does the same thing. I changed the fuse on the PCB too in case that had blown during the switch on process (tried both the spares attached the the plastic casing, there's no guarantee they were both ok, but I would be confident they haven't been changed prior and so expect them to be ok).

What do we think has happened? And...

1. If a new PCB was ordered and replaced would that suffer the same fate?
2. Are there other parts on the PCB that would prevent correct operation of the boiler if it were to match the 5 wire pump setup?
3. Am I missing some kind of reset procedure to get it working?
4. What would my rights be now that I've fitted the part and filled it with water but was not asked or offered whether it was 3 or 5 wires?
5. What's my next step?

My regret is that I didn't stop when I noticed the different wiring setup, contact the supplier and double check it would be ok, as I said, my assumption was this would be ok seeing as the board could take the 5 wire plug and I had read about the pump being upgraded. But my mom has had no heating or hot water for 5 days now and I was eager to get her back up and running.

ANY advice and thoughts welcome. Thanks in advance.

Hello, the 5 wire pump you have is fine, the additional wires are for the speed settings. The code is 178983. You probably have a loose connection in the pcb area. A couple of things though: you have worked on a gas appliance whereby removing the cover forms part of the combustion circuit - are you able to carry out basic gas safety checks? Secondly don't work on electrics unless your competent, you could end up being hurt.

He's not working on thrcombustion chamber , only the water side. The cover does not form part of the combustion chamber, if you knew that model you would know that.

You can not just wire a multi speed pump into a boiler that only has a fixed speed wiring set up, you need a fixed speed pump

Thank you for the replies.

Let's clear up the first point, yes I am a competent person, renovated my whole house from plumbing to electrics (checked and certified by an electrician thereafter), to tiling, to flooring, to plastering and everything in between as well as car mechanics, rebuilding engines etc etc. I'm not a stupid person and common sense always prevails, I will get whoever I need to get in whenever I need to get them in if I need to and respect the fact that people train to do these things.

However, changing the pump was identified as being all water side which I felt absolutely fine doing, and it went well with no leaks and no breakages with all seals replaced and parts cleaned along the way to ensure good seal.. As far as I could tell, it was a straight swap.

I would not intend to wire in anything that was not meant to be, but when I have provided exact numbers requested for the boiler, been given the part which correlates to this number and the PCB has the correct plug to connect to it... I would not assume it is incorrect.

Hence where I stand asking the questions I do. Why have I been given part 178983 (which is the only part number found anywhere that's for this boiler) and yet it cause some kind of issue?

The PCB that's in my boiler can take the 5 wire multiplug, if anything, the 3 wire plug that was in it previously looked more like it shouldn't be there, only filling just over half of the "socket". But... If there are other factors that mean it shouldn't have it, this is the info I am looking for to speak to my suppliers and figure out if they should/could have identified there being a 3 wire option that I would have then informed them as being the one I need.

there are so many Eco tec Pro boilers, if your boiler first came with a 3 wire pump , Think it was a Wilo then no you can not use a 5 wire pump

So that begs the question of why does the boiler specific number I had to provide my supplier equate to this part number of 178983 being the on stated as correct for my boiler?

Logically, there should be at least the option of 3 or 5 wire even if it was the same main part number, perhaps signified by a -3 or -5 after.

This is what's annoying me, I've provided what they asked, they gave me this, and the PCB has the correct sized plug. Why on earth would I think it to be wrong.

Whatever the case, I need to sort it. I hope they can provide some answers tomorrow.

@sbgasman might know the definitive answer he works for Valliant, Personally I have swapped 5 wire for 3 wire with great results but never 3 wire for 5 wire

Thanks for the input Ian, very much appreciated

Jajodu said:

He's not working on thrcombustion chamber , only the water side. The cover does not form part of the combustion chamber, if you knew that model you would know that.

Click to expand...

I do know the model, I work on them practically every day. I know it’s not in the combustion chamber and never said he was.

I have asked this question so many times, and even to a vaillant technical, and the answer is always the cover forms part of the combustion circuit and therefore requires 26.9 checks, so you’re saying I’m completely wrong? As for the 5 wire pump changed loads of the Wilo ones for this one and never really had a problem.

This is what's wrong with the industry and makes me hate it and my job, too many different answers and views.

Hi Novice,

Appreciate your reply. I get that there's many different views, and honestly, I'm after all of them. The boiler will be serviced and checked by a gas safe engineer once up and running for safety (it is my moms house after all, I won't take chances), but yeah, I'll give most things a go and do ample research prior to any job I've not done before. I felt that without touching part of the gas system I was competent enough to carry out the task.

If you have changed the old 3 wire Wilo pump for an updated Grundfos 5 wire pump without issue previously, that's the kind of info I'm after. As I said in another post, I would expect that having given the correct details and the fact the PCB has the correct plug for taking a 5 wire multiplug, it should work. But after carefully noting all parts I did touch during removal, ensuring I worked in reverse and didn't do anything to the electrics other than unplug the old pump from the board and plug the new one in, I'm stumped as to what might be preventing it from working. Nothing felt like it broke on the PCB when I unplugged the old pump, the new plug went in ok, there are no obvious signs of burnout on the circuits, I had no leaks, no leftover parts, all seals were replaced and all mating surfaces cleaned prior to new seals being fitted... I was honestly surprised at how well things went until that point of turning it on.

I will go and recheck everything once I get out of work today. I just want my mom to have heating and hot water again!

Just make sure you have the pump plug in the correct way around, not sure if it goes in the other way, but still worth checking. You might not have intentionally broke/moved anything, but if the wires/flex are tight to that pcb, then it might just be that. Have you also checked for voltage?

Yeah the plug can only go in one way, I did make sure that was the case. I will double check the wires haven't crimped themselves though. I haven't yet done any voltage checks, but this is where my knowledge would start to dry up and so I'll have to look at getting someone in. I can do basic checks but I think it'd be too easy for me to miss something so I'd rather someone else does this.

Post the complete model no. and GC no. of the boiler and a pic of the pcb if possible.
There have been several variants of pump model and pcb versions over the years.
It sounds as though your pcb has the single pump relay designed for a single speed 3 wire pump.
The 5 wire pumps have an additional relay on the pcb to select the 2 speeds.


There has been a distinct blurring over what constitutes a combustion chamber cover on the forum over the last few years.

The cover on an Ecotec forms part of the safety system...it's correct fitment is essential to preserve the safety of the boiler....especially on a boiler that has a history of combustion related safety issues.

Too many diyers and illegal gas workers on this forum will try and convince you otherwise.
Perhaps those yet to be convinced how critical casings are should take a look at the obsolete Netaheat boiler range...a boiler implicated in the deaths and CO poisoning of several individuals.

Given all modern boilers require specialist equipment (FGA etc) to ensure safety it is now impossible for any diyer to say that they are fully competent in boiler repair, experience in related professions is irelavant.

Hi Gasguru,

Appreciate the reply. Hopefully this works, here's a pic of the full model and GC number as well as the PCB board.