Heating OK but hot water not turning on

[JamesH1979]

I have a standard system boiler setup. I have a problem in that the hot water cylinder doesn't refill once it is emptied. eg. If my wife has a shower and empties the tank (it is only 120L and high flow shower), I then press the hot water button and the boiler does not fire up. If I turn on the heating only, or heating and hot water then the boiler turns on and fills the tank nicely, and the heating works. I wonder if there is some sort of sensor which tells the boiler that the hot water tank is empty and this isn't working?

Thanks.

 

[Masood]

The setup as you're describing it doesn't make sense. It's almost impossible to run a cylinder dry as its being constantly being replenished from the cold water storage cistern. With a high flow pump and inadequate mains flow you could be running the cistern dry, but that would not affect whether or not the boiler fires.

If by some means you are running the cylinder dry then it's possible that the boiler is not firing due to reaching the temperature set point very quickly as there is no water to conduct heat away from the cylinder heating coil, leaving a vey small circuit and no way of dissipating heat. The boiler does not fill the cylinder, nor is there a water level sensor, assuming you have a standard system boiler and vented cylinder setup.

Unvented cylinders work differently but again, the boiler doesn't have anything to do with water level, or replenishing the cylinder.

 

[SimonG]

Depends what controls you have, but sounds like cylinder stat.

 

[JamesH1979]

Sorry I wasnt clear earlier. The cylinder doesnt run dry, it is full of cold water and doent seem to trigger the boiler to replenish the hot.

 

[Masood]

Sorry I wasnt clear earlier. The cylinder doesnt run dry, it is full of cold water and doent seem to trigger the boiler to replenish the hot.

Could by cylinder stat. But if cylinder warms up when heating is turned on there's something else amiss. Do you have a 3-port valve or 2-ports? What kind of programmer? A couple of photos of the valves and related pipework would help.

 

[Destroyer2813]

What makes the clock and how old ?

 

[JamesH1979]

Thank you. I have tried to attach some photos. The cold water tank is just above the cylinder in the loft.

 

[Masood]

OK so when you want to reheat the water, you press the Hot Water Advance button? Does the LED come on?

Have you tried raising the temperature set point on the cylinder stat? Does it click at any point on the scale?

 

[JamesH1979]

Yes the LED comes on when I press it. There is a thermostat on the front/bottom of the cylinder (I thought this was for the immersion), it doesn't click when I move it round.

 

[Masood]

Yes the LED comes on when I press it. There is a thermostat on the front/bottom of the cylinder (I thought this was for the immersion), it doesn't click when I move it round.

That's the cylinder stat. It should click when you turn it past the current temperature of the water. Sounds like that's your culprit.

Although still concerning that the cylinder heats up when the heating comes on. On photo 3, that silver box on the lower of the two pipes is your 2-port valve. There is a small lever at one end of it. Have a look at it, has it been hooked over a little metal hook in the slot that the lever is in? If not, does the lever move? With resistance, or does it flop about?

 

[JamesH1979]

The leaver seems to be hooked over. I didn't want to push on it to hard as it seemed quite stiff in place.



This is the thermostat:

 

[Masood]

No, that's not hooked over, it's in the closed position.

Try turning the hot water on, turn the cylinder stat to maximum and see if the lever then moves.

 

[JamesH1979]

It hasn't moved.

 

[Masood]

It hasn't moved.

Is it still stiff, or floppy? (OOOerrr missus!)

 

[JamesH1979]

Stiff, I can't move it by hand. The end it is at says 'auto'. The other end says 'manual'.

 

[Masood]

Stiff, I can't move it by hand. The end it is at says 'auto'. The other end says 'manual'.

Then it's almost 100% the cylinder stat. And the fact that you can't move the lever at all suggests it's seized in the open position, which is why the cylinder heats up when heating is on.

I suggest getting a competent heating engineer in to swap the stat and possibly the 2-port valve out, and give the system configuration a once-over.

 

[JamesH1979]

Thank you.