Hi everyone - we’ve recently had a 5kw unit put in - generally it’s going ok, just squashing issues.
The problem is that the hot water cycle starts when it shouldn’t, always for 4 - 6 mins. Not a massive problem, but it is knocking the heating out of it’s stride to do this and reducing efficiency for no reason. Installer wasn’t sure - hadn’t seen it before.
We have it on a schedule from 13:00 to 14:30 - it’s also set to balanced mode, though we’ve had this issue on eco too. The problem manifests after we’ve drawn some hot water - a 6 minute shower or a small bath. There’s nothing in the app beyond setting the mode. The sensoComfort unit also doesn’t seem to have anything - max charge time was 2 hours - I disabled it and also set the wait period from 5 to mins to 0, as this correlated with the timings I saw, but it did nothing.
I noticed this too; it seems to be a frost protection which kicks in if the cylinder stat gets down to 10°C. I’m not sure why it would be set to such a high temperature.
I spoke to John Cassells, Twitter’s resident Vaillant controls expert, and he said there isn’t any way to change this.
It caused me major problems with my plate heat exchanger cylinder setup, because it would run the pump just enough to destratify the cylinder, but not enough to reheat it. I ended up moving the cylinder temperature sensor higher up on the cylinder so that unmixed cold water never reaches it.
I didn’t yet That installation currently loads a very basic originally electric cilinder and uses the DHW inlet (bottom) and outlet (top) to load. It works, but it cannot be partially loaded which is not ideal in more situations than I anticipated. The plan is to replace the cilinder with one that has more connections so the plate heat exchanger can circulate only at the bottom. That should fix the destratification issue and also make it more efficient.
That’s the same setup as mine. Big disadvantage is I have to make sure DHW is never scheduled to run when someone could be using the shower, because it will pump cold from the bottom of the table straight into the DHW outlet. But the tank isn’t quite big enough, so I need daytime reheats!
And because I’ve had to move the temperature sensor higher up, a reheat won’t be triggered until at least half the hot water has been used up, so it increases the chances of running out of hot water. I might swap it to a standard heat pump cylinder eventually because I think it’ll cause future occupants problems.
That’s a good idea. I’m going to do this as well while the old cilinder is still in place. Luckily that is a 300l one so it is usually ok to only load it during the night. But sometimes it isn’t…
If the bottom inlet is large enough, a reduction tee can be modified so a 15mm pipe is inside the 22mm pipe. This converts a single connection into two connections, the inner pipe can be long enough to reach other side of tank.
There also also fittings that let you add a outlet to a vented (low pressure) copper DHW tank.
Look at “Essex flange”, " York Flange", “Warix Flange”, they are all normal used to get a separate DHW outlet for a pumped shower. But I see no reason they can’t be used at bottom of tank rather then top.
(But check if your cold water inlet is just a simple connector on the tank, or if there is a pipe and diverter plate on the inside of the tank.)
If the Screw-in circulation return you found can be made long enough then it could nicely put the return from your PHE near bottom of tank.
The traditional solution is to file the “Pipe Stop” out from the middle of a “Reducing Coupling” so the 15mm pipe can continue inside the 22mm pipe, and combine with a 22mm tee, or do likewise with the corect “reducing tee”.
Thanks all for the input - if anything I’ve helped spur some useful conversation
Having played with a bunch of settings, it does indeed look like the tank is “destratifying” after the tank is half-drawn and a few litres are pulled. The only workaround I can think of is tricking the controller to temporarily thinking there is no tank attached - this might do more harm than good so am all but resigned to living with it.
That installation currently loads a very basic originally electric cilinder and uses the DHW inlet (bottom) and outlet (top) to load. It works, but it cannot be partially loaded which is not ideal in more situations than I anticipated. The plan is to replace the cilinder with one that has more connections so the plate heat exchanger can circulate only at the bottom. That should fix the destratification issue and also make it more efficient.
