under sized boiler ???

[sheff paul]

called today to give a second opinion on a recent fit,250 litre unvented hw cylinder,9 rads,most large doubles close to 16 kw output on heating side,all heating on one zone,been heated by a 18 kw sysyem boiler,not the best job.The term undersized boiler comes to mind

 

[happyflyer]

Paul,

Can you get the customer to clock the gas meter per day, perhaps its a bit late now the outside temperature is going up, but like you say it doesn't stack up, I think the 250 litre Un-vented primary coil is rated more than the boiler alone.

 

[Killy Bing]

Best remedy bar adding a second boiler or putting a bigger one in would be to wire it up as a w plan, get the cylinder to temp then heat the house

 

[sheff paul]

Paul,

Can you get the customer to clock the gas meter per day, perhaps its a bit late now the outside temperature is going up, but like you say it doesn't stack up, I think the 250 litre Un-vented primary coil is rated more than the boiler alone.

the coil is rated at 19 kw,will work ok in spring,but in winter when hw calls demand the rads will be barely warm,another 3rd rate install cannot be bothered to get involved

 

[Whyme]

That little baby got its work cut out..tell em to use the immersion.

 

[sheff paul]

That little baby got its work cut out..

I think the return temp will be pretty low

 

[albatross]

called today to give a second opinion on a recent fit,250 litre unvented hw cylinder,9 rads,most large doubles close to 16 kw output on heating side,all heating on one zone,been heated by a 18 kw sysyem boiler,not the best job.The term undersized boiler comes to mind

It should be ok. If it hasn't, fit trvs which will reduce the load. Put hot water on 24 hours so it never heats from cold. Make sure loft and cavities are fully insulated. Maybe consider weather compensation if the customer isn't thick!

 

[mfgs]

Not a very good install, but could get around it by setting the hot water and heating times separately so they aren't on at the same time.

 

[Ray Stafford]

Hang on a second.

If the cylinder is 250 litre and based on a temp rise of 40 deg C, then you should only need the full output of the boiler for just over half an hour to go from stone cold to piping hot. Whilst I agree that the rads will cool down in this time, the air temp should not drop more than a couple of degrees.

And thats assuming the worst possible scenario, of a stone cold cylinder being heated from scratch.

TBH I suspect some other problem here. You may be able to mask it by pumping up the input, but that doesnt make it the right diagnosis.

 

[Whyme]

18kw for the whole thing is crap though ray.

 

[Ray Stafford]

18kw for the whole thing is crap though ray.

Why? We used to allow 8,000 or 10,000 BTUs (BTUs, not KW) for hot water, and everyone was happy.

Sure, if I had a 16kw heating load and an unvented cyl, I would opt for a 24kw boiler. But I don't think it would be miles better than an 18kw. Better, yes. Miles better? Not really...

 

[Whyme]

i wasnt getting at ya, we dont know what the usage of the cylinder is. imho that boiler isnt big enough for the maximum output at full load.

 

[Killy Bing]

i wasnt getting at ya, we dont know what the usage of the cylinder is. imho that boiler isnt big enough for the maximum output at full load.

*Whistles*

but the boiler is good enough to do the maximum load of one OR the other.

W plan hot water priority.

 

[happyflyer]

I think the return temp will be pretty low

I think the flow temp will be pretty low

 

[AWheating]

adjust the clock so the hot water comes on at a time the heating is not required.

 

[happyflyer]

adjust the clock so the hot water comes on at a time the heating is not required.

Aw you mean have hot bath in a cold bathroom or a cold bath in a warm bathroom, electrical shower will fix that

:75:

 

[Mike Jackson]

Set the water to come on an hour before the heating. If that doesn't solve the problem then there are further problems with the install.

 

[GasmanxxxR1]

What actual problem has the customer got? I agree with Ray, it should be fine. Seen this set up many a time

 

[oz-plumber]

What temperature is the boiler set too?
It could be as simple as a faulty boiler stat.
Check the flow temp and see if it correlates with the boiler thermostat setting.
You don't need much of a temperature drop for a borderline boiler to really under perform.

Oz Plumber

 

[Killy Bing]

I must have a weird way of looking at things. I suppose during the winter the heatings been next to useless most of the time its run.

if they haven't fitted a lockshield valve to the coil then it will offer next to no resistance, easily more than half the heat will run around that and give unsatisfactory performance to both. By the time the cylinder reaches temp then the heating will be going off.

 

[AWheating]

Aw you mean have hot bath in a cold bathroom or a cold bath in a warm bathroom, electrical shower will fix that

:75:

LOL, if the cylinder is modern, it should keep warm for many, many hours. long enough for the heating to warm up 🙂

 

[Roger Welton]

Non issue in my eyes, as said just vary the timings slightly. We have the same at home boiler is currently range rated to 19kW with 15 rads (in 2 zones) and 300l unvented and we have never been cold or had no hot water.

 

[buckley plumb]

they used to say allow 2kw for the hw on vented cylinders do unvented cylinders realy need that much kw .

 

[cr0ft]

No, the modern unvented cylinders just have much more efficient heat exchangers so they can actually disperse more power into the water quicker. You could charge them with 2kw of heat from the boiler and for similar sized cylinders they would heat up in exactly the same time as an older vented one. Well a bit quicker actually due to better insulation but let's not split hairs!

 

[Whyme]

depends on the demand if its used by a few teenagers its gonna rob the heating regardless how long it heats or keeps the heat..i do like to learn and if 20kw can can heat a big house and big cylinder I'll be fitting smaller boilers in future.