JohnMo

You are just operating the boiler and the heating system all wrong. Running at the highest possible temp, then throttling everything via the trv's leads to the issue you have. Any boiler would suffer just the same, even my very sophisticated Atag boiler, I was using last year.

There are good advantages As the air enters the house it is slightly cooler than the house air, the warm air, pre heats the air so it cannot be felt. My living room terminals are at about 4m high.

Nothing unsophisticated, just simple science, if you throw lots of kW of heat at water it will overheat, unless it's moved at a fast enough rate to carry the heat away. You are basically trying to heat up everything too quickly, the trv's shut off the radiators they kill the flow route. You get the blocking alarm. No heating no DHW until lock is released. You would have the same issues with any heating device, even bigger issues with a heat pump. The alarm you get is just a low flow alarm and it locks the boiler until resolved. Our last house was 200 years old most uninsulated thick stone walls and single glazing. We never ran the boiler over 60. The only time I had issues, was when I added timers and electric trv's to the radiators. Undid what I did, never had an issue again. Run a cooler temperature for longer, will fix nearly all your issues.

Told you that very early in the thread. Obviously got shot down in flames by others, but more water volume needs to stay engaged - remove a couple more trv's or just open them to higher temperatures.

But most installed will be much lower than that. Gas up to 110% but most installed are probably nearer 80%. Had my gas boiler running at 110% efficiency measured by heat meter. Now got an ASHP and spending around £40 to 60 less in winter per month (electric and gas rates corrected). Only bit with an ASHP that isn't that good is she heating when it's cold outside. Other than that cheaper especially so if you have solar.

I was assuming Passivhaus

In a passivhaus or anything remotely close, absolutely rubbish. Fan coils - flow temp 35. CoP at -2 around 3.5, CoP at 10 deg OAT 5. UFH flow temp 30 or below CoP at -2 around 3.7, CoP at 10 deg OAT 5.7. even if you did all DHW at peak rates, you still cheaper. You can heat off peak with UFH, I currently pay about 13p per kWh. There is almost no servicing to do, look and clean radiator if required. An hour tops. UVC you would do anyway. No more than a gas boiler, possibly less. How the heck are you going to control an oil boiler, and manage heat losses into houses? with virtually no load. You would have to install a thermal store, heat to 70/80 degs for DHW then let the temp down for heating - not in the spirit of Passivhaus.

Yep

I live at in NE Scotland and use cooling, the main reason for getting a heat pump was for cooling. Doesn't really matter where you live if you have biggish windows for the view, you will get over heating. So about 30 degs?

You need the floor cool before glueing the floor covering down. Do heating should have been off a day or two before. But you need to check the screed humidity prior to doing the floor, to make sure it's below the allowable limit set by the parquet manufacturer.

Don't you need the grant prior to install. Then they would credit you £7500 against the parts you buy from them. So you never see the grant. They charge you a flat rate for design, commissioning etc.

Can't you just put the CT clamps sequential, PV first then car?

Us also. Not as good as Aircon, but does knock a couple of degrees off when needed. If you have PV generally free to use also.

A snippet from my ASHP manual, showing the service requirements. Would doubt most is actually done.

Turn key - less ventilation and any part of the heating system from what I see. Bonkers big house, bonkers big prices as you would expect. Some odd ones are "Construct internal stud wall with insulated plasterboard upto 1800mm maximum height" why insulated plasterboard on internal stud walls, and why only to 1800mm?

Except wouldn't your expansion vessel just push it's contents out the freeze valve anyway? Once it's depleted nothing else is likely to come out the system away.

A quick read of the manual The B is Fault category B (blocking faults) Blocking faults result in the heating system being shut down temporarily. The heating system restarts automatically as soon as the blocking fault is removed. Not missing point at all. It's a single boiler, that has a blocking code, this will prevent it firing up for any reason. The CH flow fault needs to be resolved with the flow through the boiler, otherwise it will only continue as it is. Would suspect the following occurs Trv's are open, boiler flows no issue, does heating and DHW as normal, trv's close in or fully closed, there is not enough flow through the system left open (2 rads and 15mm pipes), boiler gets blocking code. Boiler does fire for any reason while blocked. Rooms cool, trv's open, heating resumed as pump can now flow enough - repeat

Agreed, but trying to shove 20kW of heat via a couple of radiators and does not/isn't working, your boiler overshoots and locks you out. Once you are locked out, the boiler does not fire for heating or DHW. Nothing to do with pid controllers - just physics. Basically you have a circulation pump on the boiler it's trying to move a load of hot water, if it cannot flow through the system the boiler overheats. Is your heat system done in micro bore?

From what he says below, I don't think there is an issue with DHW only. The DHW issue is related to the boiler being in a safety lockout, due to an uncontrolled over temperature experienced during central heating duty - short cycling. The simple fix is make a larger engaged radiator circuit volume. Remove more than two trv's for example. Basically in central heating heat has a huge boiler trying to heat a cup full of water, it can't do it in a controlled way. Don't believe there is a software issue, it's a system setup issue.

Do you have trv's on every radiator?

So your heating system is locking the boiler due to short cycling, in plain English A symptom of too many zones then. Reducing the zones would therefore decrease your energy consumption also.

I would have thought the accumulator would be on the mains side. You are in effect trying to reverse flow the balance side of the system. You basically have a big accumulator attached to a small expansion vessel via the combination valve.

I use the home assistant GivEnergy API, and uses Solcast API. Once you get set up, seems in the general be quite good. But last night it was predicting 10+kWh for today, just now it's predicting 2kWh. So the charge automation is rubbish. GivEnergy API is a bit hit and miss, maybe it's just the time of year is a bit too varied.

Possibly don't qualify with when it got switched off. I only switch my heating on once a year, the same with cooling, then a thermostat does the rest. That's about the same as my non-passivhaus. I found heating our summer house with an 800W heat load expensive via a panel heater. So tied into the heat pump.

We have had a rubbish day also, solar forecast said 10+kWh generation today, so far 2kWh. Battery only charged to 70% overnight (based on forecast), so likely to use full grid cost at some point today, unless the sun pops it's head out.