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PostPosted: Tue Aug 21, 2018 8:16 pm 
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We did have a small leak which was fixed at the beginning of January this year where we were losing pressure. We lost around 1 bar in 2-3 weeks at first then 2 weeks and after a few weeks one week, then 4 days. The central heating stopped once it went below 0.8 bar.

It has now been over 7 months and the pressure gauge on our Vailant ecotec 838 plus has stayed at 1.7 bar with zero movement (I check every few weeks).

Then all of a sudden a week and a half ago we noticed after we left the living room (which does not have any radiators as it has wet underfloor heating) in the evening to go to bed that it was really hot in the house and most of the radiators were on. We have TRV valves on every radiator and they were on setting 1-3. The red light for the controller near the boiler was off so the radiators were just still warm and they could have been on a an hour or so without us entering that part of the house. The thermostat for the central heating radiators has been set to 18 degrees since May (therefore the temperature needs to go below 17 degrees to turn the boiler on for the radiators to go warm) and the temperature in the house was well over 20 degrees. The temperature was very warm for a few weeks before therefore we do not understand why the heating turned on. The thermostat has been positioned in the same place for over 6 months and I remember replacing the batteries around 6 months ago so this cannot be the issue. the termostat is one floor above the boiler on a staircase going into the loft. Maybe there was a signal issue and the heating turned on?

Anyway, I changed the setting to summer mode for a day or so then changed it back to normal. This was when I noticed the pressure had dropped to 1.6 bar and after a couple of days 1.5 bar and then 1.4 around 2 days later. Lat Thursday evening I topped up the pressure to 1.7 bar and isolated the underfloor heating by closing the valves and also closed the two valves under the boiler with an allen key. Now this is where the reverse has started to happen. On Friday after coming back from work the pressure was 1.8, then on Friday it was 1.9. On Saturday it was 2.0 and Sunday 2.1 and today 2.2. Each time I checked it was either after I came back from work before my wife and no one was at home for over 9 hours therefore the boiler was not being used. I decided to open the valves under the boiler with an allen key and once I opened the second valve I heard a sound and the pressure after a few seconds went down from 2.2 to 1.9. I then opened the valves for the underfloor heating and it remained at 1.9

Does this mean there is a problem with my boiler or is there a leak again? I do not understand why it could be a leak as the pressure was topped up to 1.7 and after a few days it increased to 2.2 (I did make sure after a few days that the filling loops were definitely closed and it did still continue to rise, however after opening the valves under the boiler I heard a sound and it did drop 0.3 bar in a few seconds, but the pressure is still 0.2 bar more than last Thursday when I topped it up from 1.4 to 1.7 bar. We did also notice one of the TRV valves was broken as the top park completely came off and I changed it with a spare one.

Any ideas or thoughts?

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PostPosted: Fri Aug 24, 2018 2:08 am 
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Quite a lot to take in there!

The radiators/heating coming on when it shouldn’t is most likely the diverter valve stuck mid position. It’s fairly common for these to fail but the can also leak and if it is the older type the water can migrate up the spindle into the motor head, which often blows the pcb as well as the head itself.

This needs checking and/or replacing asap.

The pressure rising could either be you haven’t fully shut the filling valves 100% or the filling valves are letting by. An outside chance the plate heat exchanger could be pin holed, but I would only consider this once the filling loop has been checked properly.

The latest pressure loss could be the expansion vessel has lost its pressure and when the boiler is on the pressure will rise to over 3 bar and then the prv will open slightly.

The boiler needs to be drained and the expansion vessel pressure checked and re-pressurised. I usually find this needs doing every second service on these boilers.

Again there is an outside chance that the main heat exchanger has pin holed, I have had this a couple of times, whereby the system water is going down the condensate drain so you can’t see the leak. If you can see the drain ending, check if it is constantly dripping with the boiler off for a couple of hours or more.

You need to pressurise the boiler then isolate it from the heating system via the isolation valves under the boiler. Leave it as long as possible, preferably 24 hrs or more without using it, then if the pressure drops you know there’s a problem in the boiler and if it holds but drops when you open the valves, you know it’s on the heating side somewhere.

Not much else I can add as anything else could only be checked by someone on site.

If by some strange chance the main HE has pin holed, I would always recommend getting Vaillant out on a fixed price repair, as this is cheaper than someone like me can even buy the parts for.


For this message the author gas4you has received gratitude : subsa
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