New condensing boiler - how to run it efficiently

foreversummer

Hi

I've just had a new condensing boiler fitted (traditional with hot water tank) and I am wondering how to run it most efficiently.

It is a Gloworm HX24 and my installer has set the water temperature to max (seems to be 81 degrees) and has told me not to touch it just to use the programmer. My hot water cylinder is set to 60 degrees, but the water and radiators seem very hot!

The manufacturers manual is very disappointing as it gives no indication of what the water temperature should be.

The information I have found on the net confuses me somewhat as it seems to suggest that to go into condensing mode the water temperature should be set correctly. I don't want to change the water temperature if I do not know what I am doing.

If anyone can help me understand I would much appreciate it. One thing I have noticed is that the boiler seems to fire much more than my old traditional boiler. Is this correct? I have always thought that the less a boiler fires the less gas it is using.

Foreversummer

Premier_2

The thermostat on the hot water tank will only control the temperature of the water in that tank which will be the temperature delivered to the hot taps (assuming no losses)

It won't control the temperature of the radiators as that is a separate circuit.

The purpose of the radiators is to heat the rooms, so they should be controlled by the room stat and/or radiator valves if fitted.

Is the size, measured in btu, of the new boiler the same as the old? If it's smaller, that could be one reason it is firing more often. If it's smaller, it could still be using less although its firing more often as its using less gas when it is lit compared to the old one.

Possetjohn

Hi Foreversummer,

What type of boiler did you have before? The modern boilers have a modulated burner and fan, so the heat input (and amount of gas burnt) can be varied depending on the load on the boiler. Older boilers often had on/off burners so although they fired less, they use more gas as the burner is running flat out (if that makes sense!)

I have a Valiant Combi boiler (approx 11 months old) replacing a wall hung ideal boiler with a cast iron HE and it has used approx 25% less gas in that 11 months despite a colder winter. On this one it advises you to reduce the boiler set temperature on the central heating output according to the outside temperature. i.e max (78°C) mid winter, 50°C in spring. However your boiler needs to run hotter to heat the hot water to 60°C. You could try turning it down a bit though. say 70-75°C. Also do you need the hot water at 60°C? If you can tolerate it a bit colder then it gives you more scope to adjust the boiler.

Logically the condensing boilers work best when the return water (radiators and HW tank coil) temperature is as low as possible. Thats why they are most effcient running underfloor heating systems.

Why not contact Glow-worm for advice on the best way to run it. I am sure they will be happy to help.

bluebag

I think the hot water has to be at a certain temperature in the tank to kill off things like legionella above 60 if I remember correctly.

foreversummer

Thanks guys for your help.

It seems that I should turn it down somewhat. Don't know why my installer told me to run it at the maximum.

I understand now that the return termperature needs to be low, under 57 degrees I have read on many sites to get it into condensing mode. Less chance of that I should think if it starts off at 81 degrees! No wonder it is so hot in here!

Just one other query regarding the plume - does the plume only appear when the boiler is in condensing mode as whenever I look out I seem to have quite a plume?
Foreversummer

Pssst

Did you get ALL the literature supplied with the appliance?

http://www.glow-worm.co.uk/products/flexicom_hx.asp

Turn the stat down.

To keep it simple demand>burner on>meter turns...!

Have you considered a weather compensator?

foreversummer

Hi Pssst

I did get all the literature - installation instructions left here by the installer and the user guide. Amazingly nowhere does it mention the subject of flow and return temperatures. Tells you how to set the boiler temperature, but no suggestion as to what best to set the temperature to for maximum efficiency.

Does a weather compensator actually adjust the temperature of the water leaving the boiler depending on the outside temperature? Seems like a good idea but was not offered by my installer unfortunately. I will look into that.

For now I will turn the temperature down to 70 degrees which should lower the flow temperature and hence cause the thing into condensing mode.

Many thanks
Foreversummer