I've lowered my CH water temperature - my rooms don't heat fully now - HELP

championc

Hi all,

I have changed my CH water temperature from about 70 deg to just over 50 deg. I wanted to see how my rads handled the heating of the rooms with the lower temperature, with one eye on needing a Heat Pump in the coming years. In the evening, I run the downstairs thermostats at 22 deg

I changed the temperature on 01 November.

The problem is that the rad Smart Thermostats aren't acting very smart !!! They are still acting like they are expecting the water temperature to be 70 deg, so the rooms are struggling to get over 21 deg.

I expected, after a few days, that the Smart Thermostats would dynamically adjust themselves and realise that the need to adapt, but 22 days later, it still hasn't happened. I don't want to delete and re-add my devices. Maybe does Tado Support need to clear something in the background ?

johnnyp78

All the smart thermostats do is respond to air temperature, they don’t measure water temperature nor are they aware what you’ve set your maximum flow temperature to. This might be a stupid question, but if your room isn’t heating to your target temperature, why don’t you increase the maximum flow temp?

championc

I don't think you are correct. I know I read that they learn how fast the room heats so that the valve closes before it reaches the desired temperature because it knows the heat that is discharged after the valve is closed, so that the room nicely reaches the required temperature, without overshooting by much

Unknown

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johnnyp78

@championc that may be correct, but the problem you have is that your radiators aren’t getting enough heat to reach the desired temperature. If you’re setting a thermostat to 22 and the room temperature isn’t reaching that, i’m almost certain that the trvs are remaining open but the water isn’t hot enough in the rads. Perhaps you should try increasing your maximum flow temperature and see if it helps?

championc

What I will say is that, while the temperature was set to 22 deg, the room was reading 20.4 deg, and the boiler was OFF.

I expected, if it was struggling to give enough heat, then surely the water should have been circulating?

eezytiger

From my modest understanding of these things possibilities would include....

- Property insulation inadequate

- Radiators too small

- Radiators need bleeding

- System needs flushing

- System needs balancing

- Boiler is overpowered and heating the water too fast, so it reaches thermal cutoff before the heat has made it round the system.

- Possibly other things I haven't thought of.

FWIW I have a three bed semi with solid brick walls. Glazing is a year old and top notch double/triple throughout, including doors. Loft is adequately insulated. I have been running the boiler with 50C flow temperatures since September this year and, yesterday, I dropped it to 45C. I also range rated my boiler down to 9 kW (its minimum output) over a year ago. So far, with overnight lows dropping under 5C, our comfort levels are being met. But, our temperature targets are a bit lower than yours. We have a flat 18C throughout all rooms, day and night, with bathroom and lounge boosted to 20C during the day.

EDIT : I just caught the boiler reaching 49C flow temp, despite being set to 45C. I'm aware it overshoots by a few degrees (I thought only 0-3C above) so this is the highest overshoot I've seen.

And for what it's worth, here is a flow temperature distribution so far today. Scaling is automated, so boundaries look a bit daft, but you can see that the flow temp has only been at or above target for a few minutes. More importantly, the average is comfortably under 45C, even under 40C, so a heat pump stands a real chance of working for us, at least until temperatures drop further, but I'll have the data to make a judgement

GrilledCheese2

@championc The comments above are correct. By reducing your flow temperature from 70°C to 50°C you have effectively reduced the amount of heat emitted by your radiators to 60%. So a radiator previously providing 1000 watts of heat to a room is now only providing 600 watts. That's a significant drop if the level of insulation in your home is not increased at the same time. If you want to retain the current room temperatures then try using a flow temperature of 60°C and evaluate how the system performs.

Hunter

Whilst I understand all the points above I would have also expected the boiler to be roaring, low return temp, meeting flow temp setpoint. For that temp differential from setpoint for relay the controller would be at wave 3 and continuously on. The affect of lower flow temperature in relay operation seem to be poorer control and more boiler activations when operated at low flow temperatures. What seems to happen is that when temp drops below setpoint the boiler activates for 4mins, at low SRV position. This gives limited time for the rad to heat up, this increases the number of cycle to reach set point 4 mins boiler every 20 mins (SRV with external temp sensor). This issue is made worse by low flow temps.

when my boiler cycles due to loss of flow temperature control due to min turndown, the pump will still run as long as my controller is demanding heat.

so not sure why the boiler is off and if off due to cycling the pump should be running.

eezytiger

Another point to raise is that heat pumps are designed to work low and slow - low temperatures, with big emitters, and left running more or less constantly, with only a small overnight temperature setback if you must. They are very poor/inefficient at rapidly raising temperatures and not well suited to closing a big temperature gap.

I've just had this highlighted by my own boiler system, where the new 45C limit is struggling to get my living room temp raised by just 2C. Yesterday, when I dropped the flow from 50 to 40 the house was up to temp and only temperature maintenance was required. It is a different story to increase temperature to just one room when the rest of the house is 2C cooler - and my boiler has been short cycling as a result.

Two options....

- Increase the flow temp again so that the radiator can put out more heat.

- add (in my case) the remaining downstairs rooms to the 20C temperature target. This will share the heating burden to adjacent rooms, increasing emitter volume and surface area, and avoid drafts. It will also help lower return temps and reduce the speed at which the boiler overheats.

I've chosen the second option. I'm sure it will be fine once equilibrium is reached, but a tough battle to get the temps raised in the first place.

championc

When I said that my boiler was OFF, it was totally OFF - so it was not circulating.

I changed the room and Smart TRV to 23 deg and the boiler fires, and the room heated up closer to 22 deg.

So the rads can do it, if the Smart Thermostat calls for heat.

The problem is that it's not calling for heat. It may be, to confirm my theory, that I need to set the target temperature to 23 or 23.5 deg and see what it does !!!

bendelaurence

I my experience Tado adapts to boiler setting changes pretty quickly. It’s constantly re-learning.

Can I ask, are you connected via relay or eBus?

WillYZF

I would revert to the previous setting of 70 deg restabilise mindset and then if applicable reduce by smaller increments and monitor before decreasing temperature further.