seanblee

I'm going to give that a try for a few days and see what the gas consumption looks like - at the moment, it works quite hard from 4-5:30 every morning to lift the temperature, and whilst it's been around 5 degrees outside, we've been using 85kWh a day, which feels like a lot to me.

Well, I'm still running at over 60 degrees flow temperature - I think I'm ultimately going to need to replace the two vertical radiators with bigger ones to get more heat into the room at lower flow temperatures. Other than that, I think things are looking pretty good - this is the flow temperature today, and the burner stats show it running at 28% from 4am for nearly 90 minutes, so it's no longer short cycling.

They're all back where they were, so approx 10 degrees drop across each radiator at 65 degrees flow. At this point, I think the changes that have made a difference are eliminating (most of) Evohome's TRVs, range rating, tweaking anti cycle and increasing the flow temperature. I'll give it a few days then I might try lowering the flow a few degrees in tandem with opening the lock shields a little and see what that does, but I'm happy it's at a good starting point now. Thanks again!

This morning is looking rather better: Perhaps more interesting is the burner power - this was yesterday morning: And this is today: Pretty dramatic difference! I might still raise the ACT a little to reduce the cycles when the room temperature is closer to the set point, but this is the first morning I can remember where I came downstairs to find the lounge at the target temperature, not 1-2 degrees below. 28% is as low as it'll go for range rating, the register won't accept a smaller number. It looks like it very briefly fires at a higher power level but almost immediately drops back to the configured setting.

Good call, I'm not sure why I thought 40% was minimum, I've dropped it now to 28%. I reduced the anti cycle time when I was struggling to hit the target room temperature in the lounge - I've bumped it up to 5 mins and increased the hysteresis to -15K. Behaviour on this boiler is that if the flow overshoots, both the anti cycle time and the hysteresis have to be satisfied before it re-fires. I've also increased the pump overrun from 5 to 10 minutes. Thanks again for your continued input, much appreciated!

Thanks, yes I've played with most of that. I range rated it down to the minimum (40%) for heating (installers left it on 100%). I tried decreasing the anti cycle time to 1 minute but I've bumped it back up to 3 now. On the pump, the installers left it in the default of proportional high, which was very noisy, so I dropped it back to proportional low a few weeks after it was fitted, and now it's on fixed speed pump step 2. I only got monitoring working through HA in the past few months so I've no idea if it's always behaved like this and I've just not known, or if this is something new. I can try pulling the pump and seeing what state it's in, it's internal to the boiler though so I'm not sure how easy that's going to be. I was wondering if it maybe needed a flush.

Unfortunately yes. I've increased the set point to 65 and it seems better, but I'll know more tomorrow morning - right now, the rooms have overshot their set temperature, so I think Evohome needs to re-adapt.

I increased by half a turn this morning and another quarter this afternoon (leaving some lockshields now wide open) and it hasn't made any real difference to warm-up this afternoon. The setpoint was 18 for the lounge during the day, increasing to 20 at 5pm - Evohome decides when to start warm-up so it hits this temperature at this time, and it looks like it kicked off just after 3pm today: Overnight setback for the lounge is 17 (dropping from 20 at 10pm), so there are a few spikes from 3am onwards where I guess Evohome is firing the boiler for short durations to maintain temperature. Warm-up proper started at 3:30am in order to hit 20 by 5:30am (my kids wake up annoyingly early!): I think I'm going to try that - increasing pump speed is out because it makes the whole system noisy (even with lockshields wide open), so the only logical thing to try is raising the flow temperature. I think I'll put the lockshields back where they were this morning, turn off the HA automation then bump the flow dial up to 60 and see how that runs. If it's stable, I'll start incrementally decreasing it until I get back into cycling. It does make me worry about a potential future ASHP - I know they don't need such a big delta between flow and return, but I don't see a way around a buffer without a full repipe, which would be a nightmare...

No improvement this morning. I'll try opening the lockshields half a turn as you suggest and see what that does...

I understand that Evohome turns the boiler on and off a few times an hour, but that's not the issue I'm having here - even when Evohome is continuously calling for heat, the burner is firing, the flow temperature is rapidly rising until it crosses the setpoint, then the burner is turned off until the flow falls to the hysteresis threshold of 10 degrees below the setpoint, then the cycle repeats...

No obvious improvement yet, but I'll see what it's like tomorrow morning on warm-up...

When I get a moment, I'll drain and remove the vertical rads and check the diverters - mine are a bit more awkward because I've got central flow and return via a H block valve, but there are bungs at each end of the bottom tube so I'll remove those and check.

I've removed the Evohome valves from all but the lounge radiators and put everything else back on TRV4s - that leaves Evohome controlling the two vertical rads, the boiler and the UFH (via another BDR91 to power up the zone valve, pump and actuators). I'll let you know if that helps! Should I be considering an ABV, or some sort of flow rate monitoring?

Oh, and there's no ABV on the system (one of the towel rails has no TRV). I also struggled a lot with balancing one of the tall radiators - I got to about 6 degrees drop, but if I closed the lock shield any more, the flow temperature started dropping too. I think it's near the end of the system, so maybe not enough residual head? However, it's also the noisiest if I turn the pump speed up...

Thanks folks. The Evohome is currently switching the boiler by relay and I've got a spare round thermostat, so I could try taking Evohome out of the picture and pairing that directly instead, but I think it does TPI control too. I'm not sure about the heating flow and return, it's possible it reduces to 15mm later in the run. When I balanced radiators at 65deg flow, I was going for a 10 degree drop across the rad - should I be aiming for more than that? I've got monitoring of the boiler through an EMS-ESP and that shows it dropping the burner to 28% within a few seconds but the flow temperature continues to climb rapidly (and it continues to climb for a bit after the burner is turned off too). I've tried the pump on proportional low but I'm currently running it on fixed speed step 3 (of 7) - any faster and the radiators get quite noisy.