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The cold streak at the top of the wall is, imo, being caused by cold airflow coming from the cavity in the outside wall, and that’s being drawn up to the ridge by draughts / convection. Dropping the ceiling (on the vekux elevation) would do very little afaic, as the thermal image doesn’t show this section to be adversely cold. You pointed the IR camera at purple, but there’s black which will be colder again, and as heat rises in the room that should be the same surface temp as the ceilings, but it’s not. You can use ‘tapping on the wall’ to located the dabs, plus possibly also the IR camera. You can then drill 6mm holes in the wall between dabs and inject expanding foam. This would fill voids without removing the PB. This would need to be done well, right into the corners, and all the way down each side at the internal junction with the outside wall, in order to have any practical effect. Skirting boards can come off and you can foam behind there too, if the issue is more persistent, as an additional way to attack this without doing major work. The object would be to stop airflow (thermal tenting) behind the PB, which then sucks the heated air out of the room and blows it to the ridge and to the clouds (24/7/365). The significance of the cold at the top of that wall suggests there’s a massive cold bridge, or there’s a LOT of cold air blowing a hooly through there. Ventilation heat loss (blowing a hooly) is where my money would be. The least intrusive way to see what going on at the top of that wall would be to remove some roof tiles, and peel back the membrane, and get in there from above. May just need some more rockwool stuffing in there, but it would need to be done carefully to not make it worse…..eg you stop the cold air flow but then the insulation bridges damp. Hope that’s cheered you up!!

Are all your radiator lock shields closed too far, so little or no water flows through system? Are you certain you don't have a valve closed somewhere?

A year on almost to the day and I have the same issue. did you get this resolved at all?

They do, eventually. The type 22's get warm within maybe 20mins, the triple column designer rads get warm after maybe 40mins. When I say warm, their temperature is consistent with the flow pipe reading, all around low 50's.... whereas the boiler ofcourse is showing much higher. Towel rad does get hot yes. I've tried it on and off, didn't seen to make a diff.

So next question, which you may have already said, but I can't recall, is if your radiators get warm at all? And does the towel rad serving as bypass get warm too?

Hey @Nickfromwales thanks for the reply. I put a video on Vimeo of the valves under the boiler, and the mag filter etc, those are the only valves I can see physically. It is overshooting yes. In normal operation, it sometimes goes as high as 6'c over target and flicks the burner off for a minute or so. The temperature rapidly drops during that minute. Then when it comes back on its a very low% burner output and creeps back up to target temp then stays there pretty stabley. But still with the 20'c differential between LCD display and flow pipe. I hope you're right. Let me know if anything looks untoward in the video link above. Sorry if i've not given a clear picture on the situation. it is turning into a bit of a saga and apologies for that. I will say see my other post above this one with the update from the WB guy, it is now showing a new symtpom too after he did a software update and told us to set the target tempt to 80 rather than 70. The problem still does persist with big differential between boiler and flow pipe. But its now also showing a new symptom where the boiler is getting to 80 target, then going into this weird mode for an hour or so where its constantly alternating between 20/80% burner output while the target temp stays around 80. Flow pipe is showing around 60 during this time. But this is now a new problem after the WB guy updated the software, replaced the pump and sensors. As above. before it was doing this new symtpom, yes it'd get to 70 within 10-15mins and often overshoot it by upto 6c

Yes exactly

I watched the video. That’s basically kettling, in a more modern sense of it. Shooting up, nowhere to go, shooting back down again.

Hey @SimonD thanks for the reply. It does short cycle when I run it in chimney sweep mode. When it exceeds 88'c it clips out. Even when not in sweep mode, it does overshoot the target temp by 6'c sometimes, causing it to turn the burner off for 2mins. As a safety thing I think. Also in my last post above, i added a video of a new symptom it's doing. After the WB visit, it's now getting to target temp of 80 (as suggested we do that by WB guy) then constantly changing between 20/80% burner output. You can hear it loading up and loading down as many as three times per minute. Its not cycling the burner off during that time, but definitely does not look or feel correct or normal in any way. There is no ABV on the system. The boiler doesn't have one internally.... and externally the fitter back then (2yrs ago now or so) said as we have a towel rad with no TRV, it's fine to use that with no ABV. Good question. The flow pipe at 53/54 the return tops out at around 42. Generally speaking the delta stays at 20 ish or so for a while, then after the first hour once the flow stops climbing, the return closes the delta down to 12ish, worst case sometimes as low as 9ish if I leave the boiler on for ages.

Thanks Nick, that's great. What would I be looking to find out/establish? The wall is dot and dab both sides I think (same as the external walls of the extension), and from that thermal image it almost looks to me (admitedly clueless) like they extended the internal wall with breeze blocks or similar? If so, what would some possible remedies be? Do you reckon it'd be possible/advantageous to lower the kitchen ceiling so it's flat (like the lounge behind), so that it can take more insulation? Or would the Velux make that pointless or too complex? And should the existing dot and dab inside the extension come off, and be redone in a more insulated/draughtproof way? I'm guessing you can't just fill behind the plasterboad very well without it all coming off?

Hey all, thanks for all the replies. I didn't expect it to be this popular. I'll start replying now in order. Massively appreciate the responses. I'll start working through them now. Before I do though, quick update, I had a WB engineer here today to swap the pump and sensors to rule those out. He has, and the problem has persisted. He also said something which I completely disagree with albeit me not being technical. He said there should be a different between LCD display target temp, and actual system temp. I said by as much as 20degrees?! he said the boiler target temp isnt you setting the temp for the system its just the internal temperature of the Hex. he advised we simply turn the target flow temp on the boiler up to 80. Which also sounds bizarre to me, but giving it a try. The same problem persists, 20odd degree differential between boiler temp and temp on flow pipe. (BTW i've measured the flow pipe now with 4 different instruments, including a rental expensive one, and the one Wb brought with them) they all say the same number. and that number is consistent with all the flow pipes on each of the rads. They're all within a few degrees of each other. But the boiler is the one that's 20 or so above everything else. Anyway, the stuff the WB guy did was, software update, factory settings, replacement pump and sensors, checked the hex and said it was clear, and also set the target temp to 80. Same problem persists, and a new problem has arisen now too which i'll put a video below of. After half hour the boiler gets to target temp of 80, then from half an hour to an hour afterwards it then constantly alternates between 20/80% burner output. Gradually with that window getting smaller 30/70 - 35/65 etc, then eventually settles on 45% stabley. Im not sure if this is the massive flow temp now, or the factory reset, or the new parts. But it definitely is a new thing that wasn't happening before. Would this help suggest to any of you what the problem is? Its not cycling the burner off per sae, but almost as if it cant decide what to do with the heat etc. video below.

PM'ed you Tim.

Good call on that as a potential reason but the system and boiler are relatively new I wouldn't expect it to be clogged up like mine was once

As per subject. Looking for recommendations in North Somerset/Bristol region please. Considering changing plans from renovation to replacement dwelling, using modular build but same drawings. Initial approval took more than 2 years so we are wondering how likely the planners are to present problems, given that the ecology, objections etc are all dealt with and situation is unchanged. TIA

Nah, I've had these 8000s go over 100C when there's insufficient flow and call for heat. The bangs are really quite scary! Yes, and it may be that if the boiler is able to modulate down in time, that's why we haven't heard to op tell us it sounds like the boiler is blowing up and switching off.

I say it’s creeping out, vs going somewhere. These are my assumptions from the info I’m seeing. First place I’d look would be isolation valves. Then I’d switch off every rad. Then I’d fully open both valves of the rad nearest the boiler. Then do the observations over again to see what is actually going on here. Another option is a duff pump. Another, which I’ve had with WB before, is the pump relay on the PCB giving sporadic intermittent power out, like a child flicking a light switch to annoy you, which took ages to figure out. Kept the pump active just enough to have the boiler fooled, so it didn’t lock out. Temp was bobbing up and down like a yo-yo.

@EinTopaz probably needs to explain this better - right now it reads that the boiler is running for 10 mins and reaching it's target before overshooting I fail to understand how a flow pipe leaving the boiler can be 30 deg lower than the water temp reached inside the boiler - it's likely to be 30-40 cm of pipe max so unless it's going via a blast freezer there is heat going somewhere

10 mins of doing what I suggested its doing, means it’s short cycling excessively, repeatedly, over the stated 10 mins that we’ve been shared info on.

10 mins to overheat that's not exactly a short cycle scenario IMO.............. My old glow worm 24kW with a min of 10kW could heat up, overshoot and shut down in less than 4 mins if the house was up to temp and so not a lot of heat transfer going on from the rads. The water leaving the boiler would be same temp as the display said it was!!! Here it seems to be a big disconnect that doesn't make sense

At 15.8° at that height, it’s time to get the padsaw out and cut some exploration holes. Borescopes are cheap on Amazon, which means only having to drill 10mm holes to go poking around. Looks like cold airflow from the cavity into the roof, which is typical of this type of building ‘improvement’ work tbh. Zero thermal detailing or prevention of draughts etc, just straight painted plasterboards which look nice but are used to hide laziness or sins.

Out of the running for being used I guess. Kinda reduces options to….?

👆👆👆

Not sure what you mean here? Disqualified from what?

It’s not going anywhere. Light, overheat, shut off, cool down a bit, repeat.

The boiler would shut down the burner way in advance of reaching 70° though, if there’s any discernible flow out to a circuit getting rid of heat? This looks like it ‘kettles’ quite soon after the burner ignites and there’s an unavoidable overshoot.