Oil Combi Boiler - Runs out of hot water

[wcavanagh]

Hi all,

I have a 2 year old Worchster Greenslave 2 12/18 that seems to run out of hot water after a long shower. Is it posable to get larger jets or anything to deliver more hot water? Or is it a whole boiler change?

 

[rbranco]

First check if its been de-rated, some of the oil burners have a way to range them.

But a combi should not run out of water as long as the total flow rate of HW is not greater than the specs for the boiler.
You need to get a bucket and check how many litres you get in 60seconds, or work it out the other way a full bucket vs time and work it out to 60s.
You could try turning down the flow rate to the shower.

Other than that you would need to replace boiler but then you may get into issues of sizing to the house CH demands as oil can not modulate like gas boilers.
Or consider getting an electric shower instead.

 

[wcavanagh]

Thanks, thats the problem, the boiler was sized for out new build, super insulated, unfloor heated house. The shower is hot for about 10mins, but then cools right down. If i leave it 10mins and try again, same cycle.

 

[rbranco]

I do not think that oil combis are a great idea due to this sort of problem.

Replace the shower for an electric one and just use combi for the sinks then or slow the water flow, the specs show 15L/min (+/- 15%) for that boiler and I suspect it is HW priority.

 

[BoilerBob]

Check if the flow switch is faulty first then check if the boiler stat is turned up to what it should be then check the Dow stat is turned up there are many things that can cause this all that’s needed is sensible fault finding. Bob

 

[rbranco]

Could be a fault, I would not see why it runs for say 10 mins then gets cold, I do not think that is a storage combi, but if it is then it could explain the time it takes, normally flow rate issues you would notice quickly.

 

[Terrywookfit]

So 15 l min at 40° rise for 90 litr = 6 minutes assuming boiler is set for 18 kw.
If house is tiny and well insulated it may be set for 12 kw.
Once store is depleted it will cool.

 

[muggles]

Sounds like you've just discovered the limitations of your boiler. They have a small internal store to provide hot water at a higher flow rate than they would otherwise be capable of. Once that store is depleted it must re-charge to be able to deliver the same flow rate. Once it's depleted, you can still get hot water but you need to significantly reduce the flow of water exiting the tap/shower to do so. Bigger boiler or a cylinder are the solutions. A cylinder is preferable.

 

[rbranco]

Sounds like you've just discovered the limitations of your boiler. They have a small internal store to provide hot water at a higher flow rate than they would otherwise be capable of. Once that store is depleted it must re-charge to be able to deliver the same flow rate. Once it's depleted, you can still get hot water but you need to significantly reduce the flow of water exiting the tap/shower to do so. Bigger boiler or a cylinder are the solutions. A cylinder is preferable.

Not quite a combi, they are not very clear in their documentation, nor do they state its size in the install docs. I googled a bit and found its about 45liters and has a flow sensor, when you open taps it will not fire up but if its higher flow rates such as shower boiler will fire up but clearly it can not keep the heat up long enough for extended showers.
You could try making sure ECO mode is also turned off as it will keep the tank warmed up all the time and might go longer.... or have shorter showers.

 

[Terrywookfit]

If he is depleting 90 litres + for a shower then maybe he should have a bath.

 

[oilhead]

Measure the water output of your shower and compare it to the rated performance of your boiler. Don't forget it will only give temperature figure for a given quantity and water is cold at this time of year.)This will identify if you have a boiler problem.