Water from hot tap fluctuates between hot and cold

Hi

I have an Ecotec Vaillant boiler and a Range tank. Its a unvented system. For some reason the water i get from my hot taps vary from very cold to very hot. The pipes around the tank seem hot.

The heating seems to be working.

Any ideas what could be causing this.

Thanks


Jazz

Possibly cross-over of cold to hot water though a shower mixer. See if yours has isolation valves you can shut, as a test.

It's less likely if the unvented cylinder was plumbed in properly, so H and C pressures would be identical. Often they aren't.

Thanks Chris

I was wondering if it could be a safety device in the cylinder to prevent excessively hot water coming out. We had some work done on the boiler a few weeks ago, and I think he may have turned up the boiler temp up and/or the cylinder thermostat up. With the recent hot weather, I wonder if it was over heating.

I turned down both controls a little and emptied the tank last night (in the hope of cooling the system down), and hopefully test this morning.

Just depressed that we're off to London for Sat/Sun, hardly ever get out, and this has happened.

Cheers

Sorry Chris, you were spot one. My shower mixer is crossing the water. The problem seemed to sort its self out last month, and I wrongly assumed it was by turning the temp down on boiler and tank.

It reared itself on Friday night and BG man said it was most likely what you said. To be honest, didn't really understand it when you mentioned it, and though the temp adjustments fixed it.

I played around with all fittings and definitely know its the shower now, because it affects hot water to bathroom tap, when hot water is switched off.

I can't access the isolate valves, without knocking some plaster out (wrong I know), but I can access the pipes a little easier. I'm going to speak to crossover who make the shower valve to see what they say, but another idea was to stick single/double check valves inline.