No Hot Water But Boiler Works

[dode74]

Hi all

So I have a Worcester Greenstar FS30CDi boiler as part of a closed hot water system. It feeds into a Gledhill StainlessLite cylinder with an immersion heater.

I've just been on holiday for a couple of weeks and have come back to find that there is no hot water without using the immersion heater. Originally we got cold water, so I tried running the tank (with the timer set manually on) but had no luck, so I switched on the immersion heater and several hours later got hot water. So far so good, I thought, assuming the boiler would then do its job and top up with hot water as required (the timer is set correctly to come on in the morning for shower time and in the evening for the kids' baths). It didn't, and after the baths we were out of hot water. On went the immersion heater again.

While I had the taps running I took a look at the boiler. The display shows the water temperature correctly,the pilot light indicator comes on when the temperature drops to 63°C, there is no fault indicator on the boiler and the pipes behind the fascia are all hot to the touch.
The thermostat on the tank is set to about 60°C as well and there is water in it - I tested the overflow valve.

It seems to me that the boiler is not heating the water coming into it, but all the indications I have suggest otherwise: the boiler seems, to me, to be working normally. Does anyone have any ideas, as I am stumped and want to know if I am doing something dumb before I call a plumber out.

Thanks

[The Builder]

So what you're saying is that the immersion heats the water, but the boiler doesn't.

Difficult to diagnose from here because it all depends on how the system is set up. It may well be that there is a cylinder stat on the immersion. Not the one in the element, but a separate one that tells the boiler when to heat up the water.

HW usually has preference over the CH. In your case, it's not responding. Have a look around the cylinder for a stat of some kind. It may simply need turning up or replacing. I'm going by experience of conventional cylinders here. If you have an unvented cylinder (HW comes out at full mains pressure), then it may be more complicated and would certainly need someone to look at it to investigate.

[dode74]

Thanks for the response.

There is only one thermostat on the cylinder and it is set to 60°C. It appears to be the element stat.

It is an unvented system. We replaced the entire old vented system just over a year ago when we moved in.

[buildersmate]

So have you got a three port valve that switches the flow of hot water in the closed primary system such that it either feeds the pipework into the DHW tank or the CH system or both, depending on the call it gets from the thermostats. Maybe that is not turning.