Air being vented into Open Vented CH system, advice

[rrwfotr]

I have a potterton profile 80e

I have 11 rads in total 8 of the are double skinned wth two large double skinned ones in reception rooms (the ones that only heat half way
). The boiler is about 10 - 15 years old the specs are:

Manufacturer Potterton
Model Profile 80e
Fuel Type Gas
Boiler Type Conventional
Method Non-Condensing
Flue Type Room-Sealed
Fan Fan Assisted
Output (kW) 17.58 - 23.45
Manufactured From/To 1988 - 2001

 

[D_Hailsham]

I have 11 rads in total 8 of the are double skinned wth two large double skinned ones in reception rooms (the ones that only heat half way

Thanks for the boiler info. Unfortunately the number of rads doesn't help very much. What is needed is the approximate total heat output of the rads. The easiest way to find this is to use the Stelrad Elite Catalogue.

 

[twgas]

Unfortunately the number of rads doesn't help very much. What is needed is the approximate total heat output of the rads. The easiest way to find this is to use the Stelrad Elite Catalogue.

but at least we can be pretty sure a 15/50 should be ok (unless maybe all the rads are huge which is unlikely).
Still looks a prime candidate for balancing or sludge.

 

[D_Hailsham]

but at least we can be pretty sure a 15/50 should be ok (unless maybe all the rads are huge which is unlikely).

It will all depend on the index circuit. At max output the flow rate is 1.8m³/hr, so the 15/50 has only 2 metres head available when set to speed 3; the 15/60 has 2.75m available.

If I set the boiler to maxium output are there any issues / problems I may have? I have a room themostat which I can use/set.

No problems at all. You should be using your room stat to set the temperature.

 

[rrwfotr]

I have 11 rads in total 8 of the are double skinned wth two large double skinned ones in reception rooms (the ones that only heat half way

Thanks for the boiler info. Unfortunately the number of rads doesn't help very much. What is needed is the approximate total heat output of the rads. The easiest way to find this is to use the Stelrad Elite Catalogue.

I've estimated that my rads KWH = 15.220352958 (using Stelrad Elite Catalogue figures).

 

[D_Hailsham]

I've estimated that my rads KWH = 15.220352958 (using Stelrad Elite Catalogue figures).

To nine decimal places- that's impressive. How on earth did you get that degree of accuracy?

OK lets say 15kW add on 2kW for the hot water cylinder means you need a 17kW boiler. The Profile 80E can be range rated between 17.58 and 23.45kW. It is probably still at the maximum setting.

 

[rrwfotr]

I got the figure by using a btu to kwh formula.

With regards to reply are you saying that my boiler is probably the near max for the rad's I have, also as the boiler stat is set to 3, the boiler stat is incorrectly configured?

 

[JohnD]

D-H, is it a problem if the boiler output is rated higher than the rad demand? As this is not a condensing boiler, and contains a heavy iron HEX, would it be a problem if it just cycles on and off? I am interested because my old mum's house has a Profile 100E, and once it has got the rads up to temp it just cycles to keep them there.

 

[D_Hailsham]

I got the figure by using a btu to kwh formula.

But the Stelrad Elite catalogue shows both watts and BTU!!!

With regards to reply are you saying that my boiler is probably the near max for the rad's I have

No. The Profile 80e boiler can be set to three different outputs: 17.58kW; 20.52kW and 23.45kW. I am suggesting that your boiler is probably set to the highest output. As you only need 17kW it can be adjusted by an RGI down to the lowest output. The boiler will then match the radiators.

You can check the setting yourself by gas rating. Turn your boiler on and run it for a few minutes then take a reading of the gas meter (you need all figures, not just the black ones). Leave the boiler running for two minutes then take another reading. Subtract one figure from the other and multiply the result by 30. This will give you the consumption in cubic feet or cubic metres per hour. On a metric meter the black numbers are cubic metres, the red figures are tenths and hundredths. On a cubic ft meter, each digit on the right hand black number means one hundred cubic feet, the red numbers are 10 cubic feet and one cubic feet.

So:

Metric : 1234 56 = 1234.56 cubic metres
Imperial: 1234 56 = 123,456 cubic feet

The relevant figures for your boiler are:

17.58kW = 2.18 cubic metres/hr or 77.1 cubic ft/hr
20.52kW = 2.5 cubic metres/hr or 88.4 cubic ft/hr
23.45kW = 2.82 cubic metres/hr or 99.71 cubic ft/hr

also as the boiler stat is set to 3, the boiler stat is incorrectly configured?

The boiler stat controls the temperature of the water leaving the boiler. 1 = 55C and Max = 82C. Assuming the control is linear, a setting of 3 is about 66C. This is too low. Did you set the boiler to 3 or has it always been on this setting? If it has always been on 3, it is another pointer to the boiler's output being too high.

If you gas rate test shows that the boiler is still on max output, the first thing to do is get it adjusted to the lowest output. You can then try setting the boiler thermostat to a higher output.

 

[D_Hailsham]

D-H, is it a problem if the boiler output is rated higher than the rad demand?

If you are pumping 25kW into a system which can only dissipate 15kW, the temperature will rise very quickly, so the boiler will cycle more frequently. If you match input and output the boiler will not cycle so much. Of course this is only true when the outside temperature is -1C or whatever was chosen as the design temperature. But considering that the boiler may only spend 5-10% of its time at max output, most of the time it will be cycling may be 5% on, 95% off.

The other thing to remember is that the flow rate required depends on the boiler output, so this means a different pump setting. A 25kW boiler needs 32.5 litres/minute, while a 15kW needs only 19.5 litres/minute. It could also mean a lower output pump, e.g. 15/50 instead of a 15/60.

 

[JohnD]

so is cycling a Bad Thing on a non-condensing boiler?

I know my mum's boiler stat is set to 3, this is a hangover from the days when it had gravity HW, and the taps got excessively hot on higher settings.

Cyl stat and MV fitted now so this is no longer a problem.

 

[D_Hailsham]

so is cycling a Bad Thing on a non-condensing boiler?

It's nothing to do with the type of boiler. Turning any mechanical device on and off frequently is not good for it.

As an illustration lets think of light bulbs. There have been a lot of complaints recently about companies leaving their office buildings illuminated 24/7. However many years ago, maybe 30 or more, some research was done which showed that lights left on permanently lasted much longer than ones switched on and off; and the extra cost in electricity was much less than the cost of buying new bulbs/tubes and paying someone to change them.