Bizarre Central Heating Issue

[dr_gn]

Any ideas on this:

House has a Vaillant Condensing boiler, upstars and downstairs heating circuits, and a mains pressure hot water tank. These three Circuits are controlled with electric motorised valves.

Recently, we noticed the house getting warmer than usual (about 24C instead of 20C). Adjusting the thermostats made no difference. I noticed the downstairs rads were hot, even when the room temp was 24C (normally remains spot on 20C). I thought dodgy thermostat. I decided to switch both the downstairs and upstairs circuits off completely via their respective controllers. To my amazement, the downstairs rads still got red hot. I then suspected a dodgy zone valve, but when I looked, they are both (upsatirs and downstairs circuits) in the 'CLOSED' position.

I've now switched the hot water circuit off, just to see what happens. The motorised valve for this circuit is working, because I can hear it opening anc closing as normal.

Luckily I have boiler & controls insurance, and the Vaillant technician is coming round tomorrow.

In the meantime: what on earth is going on? In the 4 years we've been in the house, it's pretty much been at a constant 20 C.

Cheers.

[Ferg]

If the motorised valve is closed, but the rads are hot it's either the valve being held slightly open by some debris OR the returns from the other heating circuit weren't commoned together before teeing into the boiler return, allowing back circulation. The latter is unlikely though because it would have always done it.

[dr_gn]

Ferg said:

If the motorised valve is closed, but the rads are hot it's either the valve being held slightly open by some debris OR the returns from the other heating circuit weren't commoned together before teeing into the boiler return, allowing back circulation. The latter is unlikely though because it would have always done it.

Hmmm. There's a little plastic tell-tale peg on the motor valves - they are both in the fully closed position. Presumably these would show up a problem? I've also got a filter on the boiler return pipe which will stop any major crud.

The returns are definitely commoned.

[dr_gn]

Downstairs circuit gets red hot when the DHW is active. The pipe exiting the valve is red hot. That valve is definitely faulty somehow. Strange about the tell-tale thing though. Any ideas?

[.:ian:.]

dr_gn said:

Downstairs circuit gets red hot when the DHW is active. The pipe exiting the valve is red hot. That valve is definitely faulty somehow. Strange about the tell-tale thing though. Any ideas?

I guess it depends what the "tell tale" thing is attached to, mine started doing the same thing as yours.
Each valve has a metal "thing" that you can manually use to open and close the valve, it seemed to be closed, but moving it by hand revealed it wasnt really, spraying a blast of silicone lube into the mechanism made it all kick in to life.