EcoTec 838 - Hot water triggers heating - **FIXED**

[fogster74]

Hi there,

A year ago we bought a repossession as our first home, with ten weeks to turn it around. We were in a rush to get in the house (we were running out of time as our tenancy was due up) when we discovered the boiler needed replacing. With limited cash, a friend offered to install the heating system as I, at the time, knew virtually nothing about plumbing - about 80% of the pipework was replaced, along with 4 of 7 rads and a new EcoTec Vaillant 838 Exclusive boiler installed. Yes, the boiler is hugely overspecced for the house, but we wanted a good flow rate for the shower and it's range rated down on the heating side. The gas side of things was seen to and signed off by a GasSafe engineer, and we were happy. For a bit...

After about 2 months we started having an issue with the boiler - Vaillant came out (the guy was great) and he was surprised to see the boiler quite mucky. Looking back though I wish I'd ripped out all of the rads and replaced all pipework not buried in concrete, but we didn't. The Vaillant chap replaced the pressure valve and suggest I get a Fernox TF1 or similar. This I did, and I started teaching myself about the heating system. Since then, I've slowly been replacing all the old rads as money permits, each time draining down / washing through the TF1, emptied the system, washed through from the filling loop on the boiler (out of a tail on one of the rads), then treated the system with Sentinel x400 (having left it in for weeks at the time) ready for the eventual final flush when all rads were done and final treatment with inhibitor.

The one thing I absolutely kick myself for is that I didn't add X100 last time I flushed out the x400 - I'd planned on removing the rads only a week or so after the last x400 flush and rinsing them through with a hose before refitting but work went crazy and I never got around to it, meaning the system probably ran for 5 months with neither system cleaner nor inhibitor in it until I rinsed them last weekend and added X400.

The current problem
Around May when we turned the heating off and, when showering, noticed the towel radiator was getting mildly warm. It got increasingly worse until I finally called Vaillant - they initially diagnosed a faulty diverter valve, then faulty PCB. Both changed, no difference, the fault remains. The last chap commented that the water in the boiler was still a little sludgy and we should get the system cleaned before I get Vaillant back out, so I decided to finally sort it.

I drained down the system last weekend and took each radiator off the wall, removing them outside and washing them through with a hose. I got very little sludge out of them, but not much - the only slightly nasty one was the only original radiator left in the house and I don't want to change that as it's imperial not metric, a new rad will either be too small, or not fit under the window, but even then the sludge wasn't too bad. I've now treated the system with X400 and the water is running clear (albeit it was running clear previously when I washed through the system and I still got some black sludge out of some of the rads when I washed them through). I'm now going to try the mains flush as suggested on this forum (here), then I'm going to try X800, run the system hot for an hour two and mains flush a second time (Sentinel tell me x800 is not just for power flushing and should give good results with a mains flush). Post x800 treatment and second flush, I'll finish off with x100 inhibitor.

I'd love to pay for a PowerFlush but just can't afford it at the moment and, from the advice on here, a decent flush with mains (and having taken most of the radiators off and washed them through anyway) should go some way to achieving similar results.

Once all is now flushed, I'll then get Vaillant back out to the boiler. I still don't understand why the heating circuit is opening on drawing hot water when they've replaced both the diverter valve and PCB - anyone have any ideas? At least hopefully they'll then come back out to a clean system

I suppose the morale (morales?!) is (are!):

1) not replacing all the rads, or taking the time to take them off and flush them through with a hose when fitting a system, was a false economy,
2) new boilers seem very fickle with regard to even slight sludge, even when paying for a top boiler from a top manufacturer,
3) don't run a system without inhibitor - even for a short period, and
4) Fernox TF1 is awesome but no substitution for a proper flush and inhibitor
5) this forum is a godsend for advice!

I'd just welcome any comments on the above, and wanted to share the somewhat painful lessons I've learned. I'd be particularly interested to hear any comments on the diverter valve issue - I just don't see why a brand new diverter valve was not closing properly on hot water demand.

 

[The831Bunny]

An ecoTEC exclusive is basically an ecoMAX with ecoTEC logic. Hydraulically they are two different beasts. Its very possible that some muck has lodged in the internal bypass in the boiler and this can cause reverse circulation on hot water.

Ideally the bypass needs removing, cleaning and/or replacing. Unless the GS engineer is having a good day he's unlikely to do any of this under guarantee. There could also be an outside chance the DV is leaking slightly on the valve spindle and causing it to stick and pass to heating during hot water.

Even though you sound like a capable and sensible DIYer any work within the sealed casing of the boiler has to be technically undertaken by a Gassafe registered engineer. So any further advice I can give you is not allowed on this forum I'm afraid.

 

[fogster74]

Its very possible that some muck has lodged in the internal bypass in the boiler and this can cause reverse circulation on hot water.

Ideally the bypass needs removing, cleaning and/or replacing. Unless the GS engineer is having a good day he's unlikely to do any of this under guarantee. There could also be an outside chance the DV is leaking slightly on the valve spindle and causing it to stick and pass to heating during hot water.

Even though you sound like a capable and sensible DIYer any work within the sealed casing of the boiler has to be technically undertaken by a Gassafe registered engineer. So any further advice I can give you is not allowed on this forum I'm afraid.

Thanks for the response, and the warning re: opening the boiler. I won't touch anything inside the boiler casing, I'll leave that to the (certified) professionals - DIY is one thing, breaking the law is another...

I'll get Vaillant back out and see what they say. To be fair, I've had three engineers out (one for the pressure valve, two for the diverter); of the three, two have been fantastic and have done all they can, the other guy was ok but didn't seem to want to go the extra mile. As the boiler has a three year warranty, has been services after 12 months, has the TF1 fitted (properly, on the return feed after the last rad feed forks in), and has been fairly thoroughly cleaned, I hope I'll get one of the good engineers and get it sorted.

Incidentally - if this had been caused by a leaking diverter, would swapping the diverter have fixed that? If that is the case, unless the replacement diverter fitted was also faulty I'm guessing it must be something else - hence your suggestion that is could be a blocked diverter gives me something to chat to the engineer about when I'm plying him with coffee and the wife's home-made biscuits!

I'll report back with progress - and thanks again for having taken the time to reply

 

[The831Bunny]

Sorry, speed read over the fact the DV & PCB have been replaced

That only leaves the bypass to be wedged open with carp, and (rare on an 838 but possibly) the domestic plate heat exchanger blocked and causing a resistance on the primary side. The reverse circulation thing may catch out an engineer who has never seen it before.

Running neat X800 around the boiler only for an hour may help if you can't get GS to sort it. Worth a go with them first though.

 

[fogster74]

Hi,

Finally got this fixed - thought I'd share my experience.

I ended up taking all radiators off, rinsing them through with a hose, then ran x800 and mains-flushed the system under mains pressure, radiator by radiator.

This has been written by others elsewhere, but here's what I did. Note that we have a Fernox TF1 on the final rad return to the boiler - this again has proved useful!
1. I drained down the system and added a drain cock on the return to the boiler (just before our Fernox TF1)
2. I refilled the system, added the X800 and bled the rads.
3. I ran the system for about two or three hours, then switched off the boiler.
4. I closed every lockshield valve and every thermostat on every rad
5. I closed the Fernox TF1 stopcock to stop anything hitting the boiler.
6. With the boiler off and a pieve of hose attached to my new drain cock, I opened the fill loop on the boiler and, watching the pressure gauge, took the pressure up to the red (remember, the boiler was off).
7. I then opened the drain cock and blew out all the water that was sitting in the central heating pipes (or as much as I could). I left the fill loop open when doing this to increase the flush. Remember - all Rads were closed, so this was only flushing the supply and return
8. Once the water ran clear, I closed the drain cock and let the system pressurise up again
9. I then opened the thermoststat and LSV on my first rad.
10. Open the drain cock. This pushes mains pressure through the rad, clearing the gunk that may be sitting there in. Some people say you should do this with the radiators empty so the water gushes along the bottom where the sediment sits, but I didn't do this.
11. When the water runs clear, close the rad valves and repeat for the next rad (allowing the system to repressurise between each rad being flushed).
12. When finished all rads, drain the TF1 (if you have one fitted), then open the TF1 cock and all rad LSVs and thermostats. Refill system (remembering to add X100 inhibitor or similar), bless radiators, test system

The reason that you do rad by rad is so that you get a burst of mains pressure into each rad, rather than just having the pressure spread across the system. Also, I realised how stupid I'd been trying to flush earlier using a radiator drain point - being on only one branch of the system, I was probably forcing gunk back through the boiler. Adding the drain cock on the return to the boiler (before the TF1) and then closing the TF1 meant that all water had to be forced out of the drain cock, and nothing hit the boiler.

I was delighted to find the system was working perfectly - no more hot water demand causing the heating to warm!

Thanks everyone for your advice on this - seems it may well have been the diverter valve was jammed open and I'm now confident that, other than replacing the entire system, my system must be pretty clean!