Condensing Boiler temprature

FreeBear

My boiler will often continue to run for a few minutes after the set temperature has been reached - The burner shuts off, but the pump & fan continue to run. Quite normal operation it helps to keep the boiler cool and sends the heat to the radiators rather than dumping it all outside.

Most thermostats have quite a sloppy response and won't tell the boiler to stop until the room temperature is 0.5°C (or more) above the set point. Then it waits for the temperature to dip 0.5°C or more below the set point before calling for heat. For most people, a +/-0.5°C hysteresis is perfectly acceptable.

MeteredOut

FreeBear said:

My boiler will often continue to run for a few minutes after the set temperature has been reached - The burner shuts off, but the pump & fan continue to run. Quite normal operation it helps to keep the boiler cool and sends the heat to the radiators rather than dumping it all outside.

Most thermostats have quite a sloppy response and won't tell the boiler to stop until the room temperature is 0.5°C (or more) above the set point. Then it waits for the temperature to dip 0.5°C or more below the set point before calling for heat. For most people, a +/-0.5°C hysteresis is perfectly acceptable.

My Danfoss thermostat also has a feature where it won't call for heat if the local room temperature is lower than but close to the next setpoint. The manual says it does this "on mild days" but it does not have weather compensation built in, so I suspect it takes recent room temperature trend into account.

RazBurley

Lorian said:

That's what Ive been trying to say. You have a boiler that could be a combi or a system boiler but it is working as a system boiler as you have Y plan and a tank. The hot water controls on the boiler don't come in to play. If the diverter were in use in the boiler you would have hot water priority rather than Y plan but we can see you have a three port valve so it's not.

It's still possible 60c flow could be enough but you may need the program for the tank to come on for longer or at a more suitable time. When does the programmer say the water is set to heat and do how long.

It's hard to get all this right without knowing what your tank thermostat is set to (it's hiding under the red jacket somewhere DON'T pull it off)

Also helps greatly if you have a cheap led thermometer with probe where you can put the probe down the side of the tank thermostat so you have a display of the water temperature on the tank (well in one layer that's another topic)

Hi Lorian,

am i right in understanding from your comment that our boiler can be used as combi or system boiler? so if we remove the hot water cylinder then same boiler can work as combi boiler?

thank you

matelodave

Probably worth checking the actual model number of the boiler before making that assumption although the controls do look a bit like those on a combi the innards may not be.

RazBurley

matelodave said:

Probably worth checking the actual model number of the boiler before making that assumption although the controls do look a bit like those on a combi the innards may not be.

hi, thanks for your comment,

our boiler is valiant eco TEC plus 418 vu gb 186/2-O H. if that helps

matelodave

I've had a shufti at the Vaillant website but cant find any info on that particular boiler so its a bit unclear whether its a combi or a system boiler. Its possible that there are two versions but I'd suggest that they wont make a boiler that would have both functions (however I'm not a gas fitter so its just a guess).

Although, that said, it may be possible for the boiler to have been installed as a heat only unit with external controls and without the hot water function connected or enabled (it would need a separate cold water feed from the mains supply to work as a combi together with plumbing to the hot taps) However I don't know why an installer would have fitted a combi boiler with half the functionality disabled(unless he got it very cheaply) to feed a hot water tank via the heating circuit

I'd suggest that you'd need to get someone who can check out your system rather than relying on guesses from Forumites who don't have all the information either on your specific boiler or even more so on how you system has been configured and installed.

Perhaps a piccy of the underside of the boiler would help to see what pipes are connected and whether there are any unconnected pipe unions (for the direct water connections to the mains and taps)

RazBurley

matelodave said:

I've had a shufti at the Vaillant website but cant find any info on that particular boiler so its a bit unclear whether its a combi or a system boiler. Its possible that there are two versions but I'd suggest that they wont make a boiler that would have both functions (however I'm not a gas fitter so its just a guess).

Although, that said, it may be possible for the boiler to have been installed as a heat only unit with external controls and without the hot water function connected or enabled (it would need a separate cold water feed from the mains supply to work as a combi together with plumbing to the hot taps) However I don't know why an installer would have fitted a combi boiler with half the functionality disabled(unless he got it very cheaply) to feed a hot water tank via the heating circuit

I'd suggest that you'd need to get someone who can check out your system rather than relying on guesses from Forumites who don't have all the information either on your specific boiler or even more so on how you system has been configured and installed.

Perhaps a piccy of the underside of the boiler would help to see what pipes are connected and whether there are any unconnected pipe unions (for the direct water connections to the mains and taps)

Hi, thanks for your reply.

i will ask someone to have a look and advice.

i have attached pics of the underside of the boiler. it has gas pipe and a condensation plastic pipe. i am also thinking of putting 3 more radiators, do you think it will be ok for the boiler to handle an extra 3 radiators. we already have six rads at the moment.
thank you
 

Lorian

No I meant it didn't matter which it was, even if it was a combi boiler it was running in heat only mode as you have a tank. 

Now we have more info it looks like a heat only boiler 

You originally said it had a separate control for water temp - can you post a photo of the controls on the boiler?

RazBurley

Lorian said:

No I meant it didn't matter which it was, even if it was a combi boiler it was running in heat only mode as you have a tank. 

Now we have more info it looks like a heat only boiler 

You originally said it had a separate control for water temp - can you post a photo of the controls on the boiler?

i have attached the control pics. i always thought that the control with tap sign is for controlling the hot water temp but i have learnt now that it only shuts the water, The water temp and heating water temp both are controlled by heating control button.
thanks