Increased heat loss from Vaillant unvented cylinder

[joncox]

I have a S pan installation, full Valliant system (615 system boiler, 155l Unistor with NTC sensor installed, controlled by VR65 and VRC 430 weather compensation unit).

I've noticed in the last 3 days that the cylinder holds its DHW temp much less well during 'non-demand' periods.

For example, for a target DHW temp of 58 degrees until 21:30 this evening, the cylinder is now (midnight) below 40 degrees. There has been no real DHW draw off (showers, baths, whatever) in that time. Previously, I would have expected the temp to remain >50 degrees.

There are no suddenly dripping hot taps or leaking pipes that I am aware of, and the 'normal operation' green LED in the VR65 is solidly on as usual.

Conincidentally, the installer is coming Thurs for 1st annual service, but any thoughts or advice in the interim very gratefully received.

 

[twgas]

check there is no leakage from the temp/press releif, at the tundish/discharge pipe

 

[joncox]

The tundish is dry - ditto (on a basic check) the PRV copper outside.

Anyone with any further suggestions?

many thanks

 

[doitall]

Has it got a secondary circuit.

 

[Agile]

When no one has been using SHW for 30 minutes feel the outlet pipe about 1 m from the cylinder.

Also check that the boiler pump over run is not continuing past about 10 minutes.

Tony