New boiler - cold radiators

ThisIsWeird

Nnnoooooo!
Go for a laser! I mean, InfraRed - and you can 'shoot' your family with it as well. 
It'll make balancing your system enjoyable... 

FreeBear

kittennose said:

OK you've convinced me - brought 3 
Is there any rule what the incoming temp should be - assuming a CH flow temp of 60

The incoming temperature will be a couple of degrees lower than the boiler is set to. What you need to adjust is the lockshield (normally) on the outlet so that there is a 10-12° difference.

The exact calculation is:

(Tf - Tr) * 0.3 = Td

Where Tf is the flow temperature (60°C), Tr is the nominal room temperature (typically 20°C). Td being the temperature drop across the radiator.

So (60-20)*0.3 = 12°C

Note - Those ebay modules are not calibrated and will probably give different readings. So make a note of what each one displays with the sensors in a cup of water.  Pick one, and then add/subtract the difference on the other one(s).

To hold the sensor on the pipe, I found a Talon pipe clip to be ideal (see piccie up thread). Failing that, a bulldog clip will work.

ThisIsWeird

Useful info, FreeBear. 
Would you ideally choose, say, 18oC for Tr in bedrooms?
Still suggesting the IR Therm. 'click' - there you go

FreeBear

ThisIsWeird said: Would you ideally choose, say, 18oC for Tr in bedrooms?
Still suggesting the IR Therm. 'click' - there you go

The difference between 20°C and 18°C is minimal, and only equates to a change of 0.6°C for Td. Balancing radiators doesn't have to be exact, and a +/- 1°C is well within the margin of error. Close enough is good enough.

Whilst IR thermometers are handy, they don't do well aimed at small pipes, especially if they are shiny. When I've used one, it was a bit hit & miss.

kittennose

Bad news update - the heat didn't last long and now all radiators are back to lukewarm and not heating up.

I also noticed the pressure has dropped from 1.7 to 1.1 when the heating is active.  Seems a lot for just bleeding each rad a little?

I've topped it up to 1.4.

ThisIsWeird

1.1 is fine - don't increase it more than this unless there's a good reason - and there isn't.

Yes, if you bleed, your pressure will fall - that's normal.

1 bar, or fractionally above, is fine. Don't top up more than this.

Monitor the boiler's behaviour - is it still running (burner light on) when these rads go lukewarm? If so, there will be a reason. I suspect, tho' that the boiler effectively turns off, as it 'thinks' demand has been met.

How many of these rads you are tweaking have TRVs on them? I presume each one has the TRV opened fully at the moment? In fact, off with their heads.

FreeBear

kittennose said: Bad news update - the heat didn't last long and now all radiators are back to lukewarm and not heating up.

I also noticed the pressure has dropped from 1.7 to 1.1 when the heating is active.  Seems a lot for just bleeding each rad a little?

You need to check the pressure when the system is cold - Mine is currently sitting at 1.3 Bar, but had been up to 1.9 Bar earlier while the boiler was running. As for air, it did take quite a while to get all the air out. Several weeks in fact - At one point, I was suspecting a leak somewhere, but could find no evidence of one. I put it down to excess oxygen trapped in the water which was released every time the water was heated. It seems to have settled down now..

Radiator temperature - When I first started messing with my "thermostat", the boiler would run for extended periods at a very low heat output. Maximum flow temperature was set to 60°C, but the "thermostat" was only calling for ~35°C. Fixed that by setting much more aggressive PID gains and setting a minimum flow temperature of 40°C (have since dialed that back). Don't know if Nest will give you the option to set min & max flow temperatures or adjust any other parameter. That you have managed to get the radiators hot at least once leads me to suspect the Nest device.

The smarts controlling my boiler - https://github.com/FreeBear-nc/esphome-opentherm

The smarts controlling heating schedules & data logging - https://www.home-assistant.io/

Pretty graphs generated by Grafana - https://grafana.com/oss/grafana/

cheme7676

Hey @kittennose - I'm facing the exact same issue after just replacing my boiler with a brand new Viessmann Vitodens 050 35kW. Rads are taking many hours to warm up.

I was wondering if you managed to find the problem? The only thing I can think about these boilers is that they allow for 'Weather Compensation' and hence run on a 'heating curve'. Still trying to figure out how to change this

FreeBear

cheme7676 said:

Hey @kittennose - I'm facing the exact same issue after just replacing my boiler with a brand new Viessmann Vitodens 050 35kW. Rads are taking many hours to warm up.

I was wondering if you managed to find the problem? The only thing I can think about these boilers is that they allow for 'Weather Compensation' and hence run on a 'heating curve'. Still trying to figure out how to change this

Did you have an external temperature sensor installed along side the boiler (it will be a small white box mounted on the North side of the house) ?

If you have the sensor, you should be able to disable weather compensation by going in to the programming menu. Alternatively, download the ViGuide app and pair it with your boiler - The installation manual should tell you how to how to pair, as will the app. It is a bit of a pain to do, but once in, it is easier to tweak the settings.

Edit:  Ignore weather compensation & OpenTherm - In your thread on the subject (https://forums.moneysavingexpert.com/discussion/6507408/new-boiler-but-radiators-are-not-heating-up ), You don't use either.

Another thing to bear in mind is the type of thermostat that is connected. If it uses the OpenTherm interface, the radiators may not always feel particularly hot. Once my house is up to temperature, when the boiler kicks in to maintain the set point, the control only calls for a low heat (flow temperature). Today has been relatively warm, and this afternoon, the flow temperature was only ~40°C. On other (much colder) days, it would be as high as 52°C.

kittennose

cheme7676 said:

Hey @kittennose - I'm facing the exact same issue after just replacing my boiler with a brand new Viessmann Vitodens 050 35kW. Rads are taking many hours to warm up.

I was wondering if you managed to find the problem? The only thing I can think about these boilers is that they allow for 'Weather Compensation' and hence run on a 'heating curve'. Still trying to figure out how to change this

Doesn't seem as bad but to be honest I haven't paid much attention while it's been mild - we had someone over to fix some leaky rads after the installation and they seem to think it's the nature of the boiler cycling on/off and they all do it. Not sure I believe that.

I think it's more a balancing issue - I've realised our direction of flow has been switched over which is maybe why I have struggled to balance them previously.

We have no weather comp or open therm enabled (we've had 2 plumbers over who claim it's "pointless" - my translation is they have no idea how to do it).