A Well Designed Boiler

[GeorgeNewman]

I have had a Worcester Heatslave 2+ boiler for 27 years. During that time it has been serviced annually by a gas engineer.

The other day it required its first spare part - the pilot safety thermocouple failed.

Other than this minor repair it has never gone wrong or caused any trouble. I have checked its efficiency (16Kw in, 11Kw o/p to water) which is still the same as when it was new. The surplus warmth heats my drying cupboard, so its overall efficiency I estimate to be in excess of 80%. And it is nearly silent in operation.

The boiler has no electronic components.

I fear that when it finally needs replacing a new boiler will give far more trouble, and will be a net annual cost to me despite the slight improvement in efficiency from a condensing boiler. Some £3,000 to install, and a higher annual service charge even before the cost of any repairs.

And it is unlikely to last for the best part of 30 years.

It is a pity that new technology seems to offer only more complexity and cost, without giving much in the way of improvement in overall efficiency or convenience. javascript:emoticon('')
Sad

 

[D_Hailsham]

I have checked its efficiency (16Kw in, 11Kw o/p to water)

You can measure the input from the gas rate. But how did you measure the output? I would like to be able to do the same, so I can check the efficiency of my 20 year old boiler.

 

[GeorgeNewman]

Thanks for asking, D_Hailsham.

I do it as follows:

you will need a reliable thermometer, precise to 0.1 degree C, and a reasonably sized water container of known capacity - say 10L

Turn off all radiators, taps, and appliances.

Choose a hot tap for the measurement - the bath is a good choice.

Turn on the boiler.

Turn on the tap fully, or so as to get a constant rate of water flow, and leave running for at least 30 mins. This will equilibrate the thermal mass of your system - boiler, pipework, etc., and allow the hot water to reach a constant temperature.

Carefully measure the temperature of the hot water from this tap.

Then fill your water container to its known capacity, and measure the time it takes to fill.

Finally turn on your cold tap fully, and leave for a new minutes to equilibrate. Carefully measure the temperature of the cold water.

Now you have the measurements to give you the boiler output to water.

(Note: check that the boiler burner is fully lit continuously while the hot water is flowing, otherwise you will get a false result.)

This is done as follows:

Multiply the measured hot water flow rate, in cc's per second, by 4.18. (This converts calories to Joules.)

Multiply this number by the temperature difference, in degrees C, that you measured between your hot and cold water flows.

The resulting figure is the boiler output to water in Joules per second, or Watts. (Divide by 1,000 for kW.)

This is probably best done when one's wife is out, and is good fun if you happen to have a son or daughter interested in specific heat and all that!

As you say, heat input can be calculated from the gas flow rate. Check your gas bill for the exact calorific o/p factor - it varies a bit because of a small proportion of non-combustible gases such as nitrogen mixed in with the methane.

Good luck!

 

[GeorgeNewman]

PS:

I was assuming a combi boiler, not a conventional one with a hot water tank. But the method should still work - you will just require a bit longer to bring the system to thermal equilibrium, especially if the hw tank is fed from a cold water storage tank.

 

[D_Hailsham]

Got it ! You are just using the well know equation for the flow required through a boiler in reverse. So:

Q = W/(4.18 x deltaT) becomes W = Q x 4.18 x deltaT

I was assuming a combi boiler, not a conventional one with a hot water tank. But the method should still work - you will just require a bit longer to bring the system to thermal equilibrium, especially if the hw tank is fed from a cold water storage tank.

I have a conventional boiler.

I can see how your method works for a combi - the water is going into the system cold and is being heated directly. But I am unsure how it will work when you have a large cylinder full of hot water which is being drained through a tap at one end and replaced by cold water at the other. The rate of flow into the cylinder must be the same as the rate of flow out. So are you suggesting that, eventually, the temperature of the water in the cylinder will settle down to a constant value, which will be the temperature from the tap?

 

[Deleted member 105431]

Just goes to show you pay for what you get, I doubt a cheaper boiler would've been as durable or reliable over that time. I prefer the Vaillants myself but recognise that WB are quality and will outlast many cheaper boilers such as Ariston, Vokera, Elm Leblanc, Chaffeturd, Ravenheap etc etc.

 

[D_Hailsham]

Just goes to show you pay for what you get,

I think you mean: you get what you pay for or, as John Ruskin (1819-1900) said:
There is nothing in the world that some man cannot make a little worse and sell a little cheaper, and he who considers price only is that man's lawful prey

 

[GeorgeNewman]

D_Hailsham,

Yes - just that. It's a bit Heath Robinson, I know. Perhaps you will be able to experiment a bit and refine the method.

Given sufficient time, perhaps an hour or so depending upon the hot tap flow rate you set, the system should settle down to equilibrium through the boiler, hw, and cw tanks.

I, of course, have little experience of conventional boilers, having had my Worcester Engineering HS2+ one for so long...

 

[Deleted member 105431]

Just goes to show you pay for what you get,

I think you mean: you get what you pay for or, as John Ruskin (1819-1900) said:
There is nothing in the world that some man cannot make a little worse and sell a little cheaper, and he who considers price only is that man's lawful prey

yes that's exactly what I meant

 

[BigBurner]

Just goes to show you pay for what you get, I doubt a cheaper boiler would've been as durable or reliable over that time. I prefer the Vaillants myself but recognise that WB are quality and will outlast many cheaper boilers such as Ariston, Vokera, Elm Leblanc, Chaffeturd, Ravenheap etc etc.

All boilers last a lifetime if you keep changing the parts that fail. A good clean install, with a magnetic filter, and change inhibitor every 4 years will mean an average boiler will last as long as any Vaillant - which is a standard stock part kit - like a Heatline Solaris and the ECA.

I know some Ariston Microgenus combis that have been running for over 6 years without a hitch. Reasonably simple boilers.

Vaillant are middle of the road, Quality is Viessmann, Atag, Atmos, etc.

 

[Deleted member 105431]

Just goes to show you pay for what you get, I doubt a cheaper boiler would've been as durable or reliable over that time. I prefer the Vaillants myself but recognise that WB are quality and will outlast many cheaper boilers such as Ariston, Vokera, Elm Leblanc, Chaffeturd, Ravenheap etc etc.

Vaillant are middle of the road, Quality is Viessmann, Atag, Atmos, etc.

that's a matter of opinion, Viessmann, atag and atmos have very low sales volumes in comparison and are more expensive with similar performance and less availability of spares or backup should boiler breakdown.

 

[BigBurner]

Vaillant are middle of the road, Quality is Viessmann, Atag, Atmos, etc.

that's a matter of opinion,

A matter of fact if you look at the failure rates.

Viessmann, atag and atmos have very low sales volumes in comparison and are more expensive with similar performance and less availability of spares or backup should boiler breakdown.

They are still better quality. The backup is more local. If you have a good dealer then fine.

No Vaillant can look at an Atmos in design or quality.

 

[numpty1]

Just goes to show you pay for what you get, I doubt a cheaper boiler would've been as durable or reliable over that time. I prefer the Vaillants myself but recognise that WB are quality and will outlast many cheaper boilers such as Ariston, Vokera, Elm Leblanc, Chaffeturd, Ravenheap etc etc.

Vaillant are middle of the road, Quality is Viessmann, Atag, Atmos, etc.

that's a matter of opinion, Viessmann, atag and atmos have very low sales volumes in comparison and are more expensive with similar performance and less availability of spares or backup should boiler breakdown.

he has a point,went to a breakdown today MHS DUPLEX boiler,it will take fifteen days before they can get the part.boiler is only three year old.fan had sheared and got lodged in the flue about two foot from where it should be

 

[Deleted member 105431]

Vaillant are middle of the road, Quality is Viessmann, Atag, Atmos, etc.

that's a matter of opinion,

A matter of fact if you look at the failure rates.

Viessmann, atag and atmos have very low sales volumes in comparison and are more expensive with similar performance and less availability of spares or backup should boiler breakdown.

They are still better quality. The backup is more local. If you have a good dealer then fine.

No Vaillant can look at an Atmos in design or quality.

Vaillant have 250 engineers in the uk. Parts available overnight thru hrpc in most cases they are in stock. I doubt Viessman etc can beat that for local service. Where do you get your failure rates from? Vaillant nor the others publish them for obvious reasons. Quality is subjective-for instance the Viessman vitodens 100 doesn't impress me much.

 

[namsag]

Bigburner . you say matter of fact if you look at failure rates.
Can you put a link to these facts or put a picture of it if you have a publication