Oil combi boiler hot water capacity

[benwatkins]

Is it true that all oil fired combi boilers only have a limited capacity for hot water?

I can only get a couple of sinks or a very short shower out of my Boulter Camray 5 boiler before the water goes lukewarm. I always thought this was because it wasn't a very good boiler but I've been told that is normal for oil combi boilers. That they can't continually heat water to full temperature at mains pressure like a gas boiler does so they have to heat an internal tank. Does that sound right?

The reason I ask is that I need to replace the boiler and if I can't get a boiler that can supply limitless hot water at mains pressure I'm going to get a smaller central heating only boiler so I can move it to a more suitable location.

By the way, I can't have a hot water cylinder - for several reasons but mainly because my house is tiny and there's simply no room for it.

 

[Burnerman]

I would have thought that your combi was more than able to give you plenty of hot water.....my own Worcester 12/14 Heatslave can supply continuous hot water for showering, even when the incoming water temperature is as low as it is today.
I'd suggest maybe a diverter valve problem, where the hot water is going into your radiators or maybe the plate heat exchanger is furred up inside.
I assume the burner is constantly running when you are using hot water?
John

 

[benwatkins]

Thanks John. The burner is on constantly when the tap is open. I agree it could be a diverter problem. Thing is that I'm not fussed about repairing it because I need to replace the boiler for other reasons (the main one being that it is a huge floorstanding unit with an internal tank and I need either an external or wall hung compact boiler). What I really want is a combi that supplies limitless hot water without relying on a tank - like every gas combi on the market. Second choice if the first isn't available is the smallest possible central heating-only boiler I can find and I will have electric-heated hot taps and shower.

I just looked up the Worcester 12/14 Heatslave out of interest. It says it has a 15 litres per minute hot water capacity which is fine for a shower. It also has a 67 litre tank making it quite a big unit (same size as my current boiler). The manual for my boiler on the other hand doesn't give a maximum flow rate, just says it has a 40 litre tank which takes 5 minutes to heat up once drained. That explains why I only get a couple of sinks or a couple of minutes of showering before it cools down.

So I think I'm coming to the conclusion that if I want continuous hot water I need a more powerful boiler which is at least the same size as my current one with a big internal tank. UNLESS..... someone out there knows of a magic oil combi boiler that is compact and supplies 15 litres per minute (or thereabouts).

 

[oilboffin]

No the woooster won't give that amount of hot water try a grant it's a better boiler get a 21 or 26 kw
depending on the size of your house.It's true oil boilers don't modulate like gas boilers so they rely on brawn so to speak they have a heat store which gives a burst of hot water while the burners lighting up to heat the rest of the water flow.Bob

 

[muggles]

There might be a fault with the existing boiler as mentioned above. If you can find the specs, measure flow rate and volume of hot water to see if it matches up. That'll give you an idea of whether you have a faulty boiler or high expectations!

Oil combi's are a big compromise. Even brand new ones are only around 60-65% efficient when generating hot water, and all have an internal tank. If you want more flow rate at a given temperature, you need a bigger more powerful boiler, but that will of course cost more to run on heating as well.

I'm not aware of a wall-hung oil-fired combi being available. They're too big and heavy to stick on the wall. An external is probably your best bet if you're tight for space.

 

[oilhead]

An oil combi's heatstore is not a storage tank per se. It provides a supply of primary water to the plate heat exchanger, and as long as the heat exchanger is not furred up, or the diverter valve passing, or the tempering valve (if fitted) is not scaled, then your oil combi will operate very much as a gas combi. Competent servicing will keep a check on the important points.
How old is your boiler? 20 years? You would have got through 3 gas combi's in that time and had all the same problems as you now have.

 

[oilboffin]

I prefer oil boilers to gas.Bob

 

[benwatkins]

MUGGLES! Back from Finland then?

So cutting to the chase, the only way to get continuous hot water without it losing temperature is a big combi? Which for me means going external because there isn't room in the house.

The alternative is a small CH only boiler that can be hung on the wall.

 

[muggles]

MUGGLES! Back from Finland then?

So cutting to the chase, the only way to get continuous hot water without it losing temperature is a big combi? Which for me means going external because there isn't room in the house.

The alternative is a small CH only boiler that can be hung on the wall.

Yes, brought the snow back with us as well

You could have a small CH only boiler but then there's the issue of what to do for hot water of course!

 

[benwatkins]

You could have a small CH only boiler but then there's the issue of what to do for hot water of course!

My shower is already electric. I would prefer to convert it to a thermostatic mixer which is why my first choice is a combi boiler but it is looking more and more like that's not an option. Other than that it's it's just two sinks - bathroom and kitchen. I'm replacing the kitchen shortly and have gone for one of those instant hot water taps so that just leaves the bathroom. Might as well have an electric hot tap in there too.

Bloody boiler must know I'm talking about it because it has stopped working this morning! Separate post coming!