Condensing boiler temperature setting

Has anyone got any thoughts on the correct setting for the temperature dial on a condensing boiler please?

Its only marked MAX and MIN and has always been left on MAX since it was installed a few years ago. Our HW stat is on 80C, because that is what I want. Set the boiler output temperature too low and it will constantly cycle on and off unable to achieve the demand.

Suggestions and your reasoning please?

Reply to
Harry Bloomfield
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Setting it low should mean it runs continuously and if too low, will not fulfil the demand. If your HW system is designed to modify the boiler flow stat (some more sophisticated boilers allow this) you might achieve your 80C DHW (which IMHO is set too high but accept that you want what you want)

In my book the boiler needs to be set as low as possible whilst still satisfying the demand. This should keep it in condensing mode as much as possible.

Reply to
Bob Minchin

Generally the lowest flow temperature that you can get away with, and still achieve adequate heating and fast enough warm up, is the ideal. It will result in the lowest return temperature and the greatest condensing efficiency. As side benefits it also gives less creaks, clanks, and groans from the metalwork of the radiators and pipes since there is less temperature swing. Less "danger" from hot rads etc.

However the general problem with this approach is that on cold / high heat loss days you may not be able to achieve the set temperature in the house, and it poses a problem if you want to heat a cylinder to a high temperature as in the case here.

The solution to this problem is via a system that supports split temperature operation, (i.e. one that understands the difference between running rads and heating a cylinder and uses a higher flow temp for the the latter). The posh version being weather compensation, that also understands when its cold outside and makes further adjustments to the radiator flow temperature in response.

Not all boilers have the controls to do these things.

Reply to
John Rumm

With most people, the lower temperature limitation is governed by the hot water needs. Subject to the above, set it as low as you can get away with (ie keeping the house warm).

Reply to
harry

Could you name some that do ?. I will be looking for a new boiler this year, possibly, but not necessarily a combi

Reply to
Andrew

Pretty sure the Vaillant eco-tec supports split temperature. Might need an extra box for weather compensation.

Reply to
newshound

I run mine of max at all times .... control handed over to tank stat, which cuts boiler off when it reached 65 degrees

Reply to
rick

TBH I have never seen a tank stat that goes over 65 deg.

Reply to
ARW

Most Vaillant, some WB, Some Viseman, and probably quite a number of others. (I have not been looking at recent models for a few years).

Reply to
John Rumm

Drayton HTS-3 It has markings every 10C up to 80 then just a mark for

90C.

Thanks for the replies. It is just a simple basic condensing boiler, no separate sensing for HW and heating, so I am stuck with the MAX boiler setting.

Reply to
Harry Bloomfield

With your electronic skills, you should be able to modify the boiler for dual temp setting.

The sensor is usually a thermistor. I bought one as a spare part on ebay for a few quid and measured it at various temperatures and found that it closely complied with one of the standard curves for thermistor sensors.

With a relay you can switch in an extra resistor (or variable resistor) in series or parallel the flow temp sensor and drive the relay coil from the DHW demand signal to give one setting for CH and a boost for DHW.

Reply to
Bob Minchin

80C! You could almost make tea at that temperature.
Reply to
pamela

Eh ? ..... my tank stat goes up to 90

Reply to
rick

or use an IN4148 diode :-)

Reply to
rick

I run my Valliant ecotec Vaillant with HW at ~50C and CH around 60C. Have the CH low in Autumn/Spring and wind it up if necessary when it get really cold and windy. ( House is 1800 with stone rubble walls etc and thus poorly insulated)

Reply to
Robert

I would say you should be switching to a second thermostat setting, and not changing the temperature sensing, which may well do other things too such as lock-out if the boiler overheats, which you might end up defeating.

Reply to
Andrew Gabriel

I use fitted the weather compensator when I did mine. That means the heating temperature is driven by a combination of the exterior temperature and the selected "curve" in the controller. You select a curve that matches the heat loss of the house.

That means in the less cold periods it will often run flow temperatures in the 40s and 50s, and only ramp up to over 60 when it starts getting close to zero. The water however is always heated to 60, and then it does an anti salmonella cycle on Wednesdays to heat it to 70.

Reply to
John Rumm

Don't do that.

With a tank at least when the boiler goes wrong you can turn the immersion on and have a hot bath. And fill the bath in less than 20 minutes. And have the tank, not the boiler scale up...

Andy

Reply to
Vir Campestris

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