Radiators heat but water tank doesn't

[Ivan]

Hi,

I have just moved into a newly built house. The CH system is oil-fired with independent timer circuits for the hot water, upstairs radiators, and downstairs radiators.

The radiators heat fine but the hot water tank doesn't.

I have read posts on this group from people with similar problems and the main advice seems to be check the thermostat and the functioning of the valves.

I feel a bit thick here, I can't find a thermostat anywhere on the hot water tank. Should there definitely be one there? If there wasn't would this explain my problem?

Other bits of info that may be useful

- There are three valves on the water pipes around the tank with an auto and manual setting. All are in the auto setting. When moved to manual they give some resistance and will return to auto when released.

- One is on a pipe half way up the tank, if I lock this in manual then the water gets VERY hot when the heating is on.

- Immersion heater works fine.

Thanks, Ivan

[Jim Alexander]

Since its a new house maybe the stat has been omitted, perhaps inadvertantly. Follow the cables from the zone valves, particularly the one half way up the hot tank. I would expect they meet up in a junction box or wiring centre. Read the other posts to find a link to an S plan wiring diagram. If there is a tank stat it should be connected in the wiring centre where indicated in the wiring diagram. Beware the wiring is almost certainly mains voltage.

Also examine your heating timeswitch. I would expect it to have a HW setting. Make sure you select HW On and see if anything happens such as the water zone valve operating and the boiler firing. Report back if you are still stuck.

Jim A

[Heliotrope Smith]

Check that the programmer/timer is calling for hot water. Have another look around the hot water cylinder, most likely place to find the stat is about 1/4 - 1/3 up from the bottom. Apart from the immersion flex is there any other flex going to the cylinder? A thermostat could well be on the end of this.

[Ivan]

I think this is it. There are cables to each of the valves and the immersion heater. An extra cable is attached to the junction box but not connected up to anything.

I have double checked the whole tank and there is no thermostat attached anywhere.

Time for a phone call to the builder.

Thanks for the help.

[daz9643]

My hot water tank doesn't have a thermostat, the water temp is controlled by the dial on the boiler. I would suggest trying the screwfix.com forum, plumbing section.

[Jim Alexander]

A not unreasonable suggestion but in this case there would need to be a timeswitched live to the zone valve which appears not to be the case (unless the OP never selected HW at the timer). Anyway a mystery cable going nowhere has been reported.

Jim A

[Ivan]

Yip. Luckily the builder's plumber was onsite at another house today so he was able to call over and inspect the tank. The system should have had a thermostat fitted.