Greenstar Heatslave not producing vet limited amount of hot water

[Marcopf]

Hi, would be extremely grateful for any pointers on this problem

The full name of the boiler is the Worcester Greenstar Heatslave 18/25 Oil combi. The boiler has a 69L heatbank. We leave the water permanently set to on.

When I run the hot tap nearest the boiler i get hot water as expected for the first couple of minutes. At 2 mins the temperature starts to fall and by three mins the water is luke warm.

This is not enough to complete a shower without the wife having to rinse conditioner out of her hair in cold water

The boiler is firing up as soon as I start drawing water From the tap. As I understand it, you are initially drawing hot water from the heatbank and the boiler keeps replenishing that with hot water until you turn the tap off.

It seems the boiler is not able to keep up with the rate the water is required at and I’m inclined to think that the water starts getting colder after the hot water that was stored in the heatbank has been used up. If turn off the tap, the boiler keeps going for a while (topping up the heatbank, I presume) and wait for a while you can draw hot water again, but not for long.

Thanks

 

[SJB060685]

Is this a new problem? Did it use to work properly?

The heat store is NOT stored water for the taps, it is water stored at temperature to instantly supply heat running to the taps by means of a heat exchanger.

 

[Marcopf]

Hi, thanks for the information on the heat store. On the second point, we could never get enough water to use the bath and relied on a clapped out electric shower, so in August we had a shower put in that runs off the boiler. This worked well for a couple of months, but now cannot run for a normal shower length, the water goes to look warm within 3 minutes

 

[John.g]

Is Eco mode off and DHW temperature control turned to max? even the 69 litre primary heatbank on its own if set to max temperature of say 75C and using a heat exchanger if set to max temperature of say 75C should give the equivalent of 140 litres at 45C. Might be problem with Hx if in hard water area.?.

 

[SJB060685]

If this is a new problem then it could be a number of things John.
. Partially blocked hex.
. Sticky diverter valve.
. Boiler needs a service.
. Even the wrong nozzle installed on a recent service etc etc.

There is a response from the OP that hasn't been verified yet, hopefully that will give us a bit more information.

 

[Marcopf]

It’s not a new problem in that we’ve never been able to have a bath here with this boiler. When the shower replaced the bath it was good for a while now we can‘t even get a shower. The hot water tap wide open gives 15l/min for 2.5 mins before the temperature drops and by 3 mins it would get uncomfortable to stay in the shower.

I‘ve also been thinking that it’s a lot colder now than it was when we first had the shower installed in August and we’ve had the CH on on some nights as well, which would expose any issue further. One other thing is the burner fires up immediately when a tap is turned on, but tech help at Worcester say I should get 3 to 5 mins hot water before the burner kicks in

I was told it might be that the heat store isn’t being heated up and to check the sensor, stat, diverter and heat exchanger in that order. I’m going to get someone in. It’s just good to have some idea of what’s going on

Thanks

 

[SimonG]

Sounds like lack of primary water through heat exchanger.
If heatings fine then it's not the pump.
Probably the diverter.

 

[SJB060685]

It’s not a new problem in that we’ve never been able to have a bath here with this boiler. When the shower replaced the bath it was good for a while now we can‘t even get a shower. The hot water tap wide open gives 15l/min for 2.5 mins before the temperature drops and by 3 mins it would get uncomfortable to stay in the shower.

I‘ve also been thinking that it’s a lot colder now than it was when we first had the shower installed in August and we’ve had the CH on on some nights as well, which would expose any issue further. One other thing is the burner fires up immediately when a tap is turned on, but tech help at Worcester say I should get 3 to 5 mins hot water before the burner kicks in

I was told it might be that the heat store isn’t being heated up and to check the sensor, stat, diverter and heat exchanger in that order. I’m going to get someone in. It’s just good to have some idea of what’s going on

Thanks

Its most likely one of the above mentioned. My first suspicion is the diverter valve.
See if you can get by with the heating off for an hour and when the radiators are cold open a hot tap and give it 5 minutes and see if the rads start getting hot. If they do this would suggest the diverter is sticking.
There is another way to check but that would require taking the boiler cover off, which I suggest you leave to whoever attends.

 

[John.g]

Also with that flow rate of 15 LPM, the boiler should then fire continuously and not just run for a few minutes.

 

[Marcopf]

Thanks John G, that‘s what I thought

I tried turning up the HW stat to nearly max and running the hot water at 15Lpm again and it made no discernible difference in amount of HW before heat is lost

The boiler always fires up immediately whenever I turn a hot water tap on, whereas the Worcester tech support told me I should get a few minutes hot water before the burner kicks in

I also had the CH off with the boiler at max and the hot tap running full blast. The radiator next to the boiler was fully open, but I didn’t detect any heat there so does that rule out the diverter?

So all things considered what is the consensus on the problem?

Many thanks

 

[SJB060685]

If the radiator didn't start to get hot that should rule out a diverter valve.
The burner should ignite when the DHW thermostat senses a drop in temperature, this should only take a short time (providing im looking at the correct flow chart, there's a few for the heatslave models).
I still wouldn't rule out a problem with the HW heat exchanger.
When was the boiler last serviced? If a boiler is not regularly maintained then you could have problems with the nozzle output which would directly affect the thermal output, if the boiler is dirty inside this can have the same affect.

 

[John.g]

The PHE could be a problem but it was supplying "hot" water for 2.5 mins @ 15 LPM which is 38 litres of hot water so OK in some fashion but surprising that the 69 litre heat bank is then running out of hot water or only supplying cooler water for its remaining 30 litres or so.
Also re the boiler thermal output, 15 LPM should demand burner continuous running even at its full rated output of 25kw so even if its output has degraded it should still run continuously, so something is telling it to only run intermittently? The PHE temperature is also used as well as the heat bank temperature and the flow rate to determine the burner demand so possibly a problem with any one of these 3 items?. Even with no flow detected (< 2 LPM) the burner will still fire and start the circulating pump depending on the heat Bank and the PHE temperatures and some offset temperature.