Boiler water temp

david1946

My boiler changes the water temperature by itself.

When they first come on in the morning the radiators are so hot as to be almost untouchable but as the day goes on the water temperature has decreased when next the heating cycles on.

I reduced the temperature for a week but the boiler was on longer, up to an hour longer, in the morning until the thermostat temperature was reached.

After noting my usage every day for that week and comparing it to the previous week, and even the same week in previous years, there was not any noticeable reduction in gas usage, average about 55kWh a day, I just put the knob back to the position  that the plumber had set it to when the boiler was installed and let the boiler and its controls take care of the temperature of the house.

BUFF

david1946 said:

My boiler changes the water temperature by itself.

When they first come on in the morning the radiators are so hot as to be almost untouchable but as the day goes on the water temperature has decreased when next the heating cycles on.

It's quite possible that your boiler has load/weather compensating controls.

david1946 said:

After noting my usage every day for that week and comparing it to the previous week, and even the same week in previous years, there was not any noticeable reduction in gas usage, average about 55kWh a day, 

The only way that you can be sure (assuming that you used exactly the same time & temp settings as before)  is if you can also adjust for any difference in external weather & therefore demand. This strikes me as having been a mild winter so far (at least where I am).
Typically you would be expecting to see under 10% improvement & if you have weather compensating controls already much, much less than that - after all that is what they are there for. 

lohr500

Northern_Wanderer said:

Verdigris said:

Measure it. You can get an electronic thermometer for a couple of quid. Tape the thermocouple to each pipe, near the boiler, in turn and see what the differnece is.

Thanks, I will check those thermometers out.

I ordered a couple of these last year to measure our flow and return temperatures after we had a new oil boiler fitted :

https://uk.rs-online.com/web/p/dial-thermometers/4315621

There may be cheaper ones out there on Amazon and eBay, but Brannan seemed to be a reputable brand and I didn't want thermometers that needed batteries. Claimed best accuracy is +/- 4 C which I was happy with as I wanted to get our return temperature down to 40 C which is well below the 54C point at which condensing boilers can condense.

After a bit of fiddling around with the boiler thermostat, the circulation pump speed and the radiator balancing valves, I have managed to get the boiler to run with a flow of 60C and a return of 40C for most of the time. It does vary but maintains the 60/40 when running the central heating which is when it uses the greatest amount of oil and runs for the longest periods.

Being an oil boiler, it doesn't modulate the boiler temperature and hasn't got any load/weather compensation logic built into the system. 
 

worrywart_3

Excuse my ignorance I have hot water and heating temperature dials should both be on 50

coffeehound

david1946 said:
 I just put the knob back to the position  that the plumber had set it to when the boiler was installed and let the boiler and its controls take care of the temperature of the house.

I wouldn't put too much credance in what the installer set it to.  I suspect they set it high to ensure the customer isn't disappointed or thinks the boiler isn't powerful enough, resulting in call-backs

SJMALBA

FWIW, from the instruction manual for my boiler:

The boiler heating control sets the maximum flow temp; the system decides what actual flow temps are required at any given time. The boiler is >13 years old, so not necessarily 'state of the art'?

Ultrasonic

worrywart_3 said:

Excuse my ignorance I have hot water and heating temperature dials should both be on 50

The two don't need to be the same. Do you have a combi-boiler? If so set the hot water temperature to whatever you need it to be for actual use. For me it's the shower that is the limiting factor, with too low a flow temperature meaning I can't achieve a shower water pressure I'm happy with (achieved with a mix of hot and cold water). My hot water is set to 50° C with this in mind but you might find cooler works OK for you.

[Deleted User]

SJMALBA said:

FWIW, from the instruction manual for my boiler:

The boiler heating control sets the maximum flow temp; the system decides what actual flow temps are required at any given time. The boiler is >13 years old, so not necessarily 'state of the art'?

All modern boilers have a modulation ratio. For example, the new Worcester Bosch Greenstar 30kW boiler has a 1: 10 ratio. All this means is that as the heat demand reduces, the boiler will function as if it is was a smaller boiler. What will not change is the boiler flow temperature which is what is bring discussed here. It follows that if you have a properly set up heating system with a flow temperature of 75C or above, the boiler will never operate in a condensing mode. Condensing mode is just the recovery of heat from exhaust gases.

PS. Nowhere in the post above does the manual suggest variable flow temperatures. This only happens automatically when a boiler is connected to a weather compensation or an Opentherm device.

SJMALBA

I was referencing both the 'Heating economically' & 'Tips on Energy Saving' sections of the screenshot from the manual - the text display programmer (TD200) on my boiler shows 'requested flow temp' and 'actual flow temp' - as far as I can tell, the former changes as necessary up to the maximum allowed by the bolier heating control? It is used in connection with a room thermostat (RT10), so, as mentioned, the system decides... I think?

Am I correct to follow the tips on energy saving in the manual, and have the boiler heating control set at the 'normal' maximum of 6 (max. flow temp of 75C)?

Ultrasonic

SJMALBA said:

on my boiler shows 'requested flow temp' and 'actual flow temp' - as far as I can tell, the former changes as necessary up to the maximum allowed by the bolier heating control?

Isn't that just reflecting that it takes time to heat water up to the set temperature, rather than a form of optimisation?

My boiler heats the heating hot water up to about 5°C above the set flow temperature before turning the burners off.