Mattg4321

So there we have it. The thin end of the wedge as many of us predicted. Lucky I can afford PV and an inverter that accepts a generator input. Not sure how everyone firing up their own generators helps with reducing C02 though? Mad max here we come.

Agree almost entirely with @ProDave If carbon dioxide is really the biggest problem that we face and worth spending enormous amounts of money on (not inequality, lower living standards, crumbling public services and infrastructure, inflation, social cohesion etc etc) then why are we not investing heavily in nuclear. We all know that renewables can’t operate reliably in isolation. Also worth noting that in the last decade my electricity cost per unit has gone up by over 100%, with the standing charge going up by even more - far above the rate of inflation. I thought renewables were meant to be cheaper?!! No doubt some will blame Ukraine war for this as the cost of gas has risen, but we have mountains of gas of our own that we for some unknown reason refuse to extract. Far better for the planet to import LNG from Qatar and the US - make it make sense.

At a guess, when you get a restriction, the pressure created by the pump causes the water to take the path of least resistance - up the Vent pipe.

Heat exchanger wasn’t totally blocked on my boiler either. Just about heated the cylinder and got the rads hot for 20 mins or so, then went lukewarm. The USP3 is a very common pump. It won’t be the sole cause of pumping over on a system configuration and that has never previously pumped over imo. I think it’s pretty well nailed on that there’s some sort of obstruction/blockage on the primary circuit. All only in my opinion obviously.

There’s no doubt it’s a slight risk. The part could be damaged, perhaps even by plumber upon fitting - who will blame the part probably. However, if you can find someone sensible to fit it, it’s a risk worth taking imo. Those boilers are fairly bulletproof otherwise in my experience (had one in my old house for 9 years - was 14 years old in total when I sold - zero problems) and your only other option is new boiler if the heat exchanger is indeed blocked.

This is still sounding so much like my situation from a few years back. I also changed the pump as a first move. I also then cut the H section out and found it clear. I removed the mid position valve and found that clear. I then decided it was very likely the heat exchanger in the boiler as it was unlikely to be anything else stopping good circulation around the primary circuit. Also open vented systems suffer with sludge build up, and I had no magnaclean. It’s interesting that my boiler is also the same as yours. You could just replace everything to fix as plumber 3 wants, but seems wrong to me. If I was you then I’d check the ‘H’ section of pipework and if it’s clear I’d be getting the same refurbed heat exchanger that has cured my problem. Assuming you can find a plumber willing to spend a couple of hours fitting it for you that is. I twisted a mates arm (quite hard it must be said!) £150 for him and £80 for the heat exchanger- which according to him looked new.

Threatening it yes, but dates in the near future? Not that I know of. 30th June 2025 is apparently the date. To my knowledge they’ve not given a firm date before, that has then passed with the service still operational. We’ll see I suppose.

Haha LW only!

Radio 4 (which the teleswitch signal runs from) due to be switched off in June, so not too long.

Am I correct in thinking that pump over isn’t the only problem (symptom) here? The original (and also current) problem is lack of circulation and radiators not getting hot enough. Is that still the case?

I can’t see a low loss header in any of the pictures? I’m no plumber (electrician), but I’ve wired hundreds of boiler systems and investigated a lot of faults - although mostly electrical. Seen tens of UPS3 pumps on standard Y/S plan vented systems and never heard of one being the sole cause of pumping over. I pass the plumbing faults over to the plumbers I work alongside, but usually like to find out the cause once they’ve solved, for future reference. Pumping over very often seems to be a blockage and poor circulation. Blocked heat exchanger in boiler/blocked pipework usually where the close coupled tees where F&V pipes are, especially if this is one of those Myson aerjec things. Hopefully a plumber will see this and post soon

Definitely a box ticking exercise The only way it will get checked is if someone complains and the planners send someone out to look. Our tree protection plan including ramming scaffold tubes into the ground around the tree, with a barrier attached to it. No machinery or materials needed to go near the tree, so would’ve been more damage caused by following the plan. It got ignored.

Process of elimination. It generally let enough heat through to do the DHW - especially in summer. Think it used to start playing up after boiler had been running a bit. Something moving/expanding I guess, then boiler started cycling. I cut the old heat exchanger open and it was full of c&@p

Exactly what I did. My array won’t generate enough to need going above a 3.68kW inverter, but I’ve gone for 5.5kW at almost no extra cost and a bit of G99 aggro

The other thing to consider with a 3.68kW inverter and DC battery storage is that 3.68kW will be the most it will be able to supply to the house with any balance made up from the grid. So it wouldn’t be able to run a double oven with both oven elements heating for example.

Pretty well known that restricted flow can cause system to pump over into feed and expansion tank. Just in case it’s the same problem and you have a friendly heating engineer who will spend a couple of hours fitting this rather than sell you a new boiler, I’ll leave this here. 3.5 years on, mine still running well. https://www.ebay.co.uk/itm/384909057365?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=QR3vSnEVRH6&sssrc=4429486&ssuid=088jx6SbToG&var=&widget_ver=artemis&media=COPY

Is the boiler a Greenstar ‘Ri’? That’s what I have, so probably wouldn’t be surprising if it’s the same thing

Had a similar problem and eventually found it was a blocked heat exchanger on my heat only boiler. Bought reconditioned heat exchanger off eBay for £75 and got my friendly plumber to fit! Also sealed the system and pressurised only to just under 1 bar to reduce chances of leaks. This stopped air being drawn in and greatly reduces sludge build up too. Best thing we did. As above, does it happen when only DHW calling, as it should be flying round there? Although this can be tricky to work out as if it’s a partial blockage like mine was it appears to work on DHW as there’s little enough resistance in that circuit to get a reasonable flow

Depends if you like wasting your time or not I suppose. Chances of it being any of those things mentioned are pretty slim. I like to target the most likely thing first, before clutching at straws, but have already given advice earlier in the thread, that has been repeated by someone else on here. Getting up in the loft with the circuit disconnected and inspecting the installation is free and requires no insulation resistance tester. However, it’s probably still best to get hold of some proper test equipment or an electrician as ‘bang testing’ isn’t really something to be advised.

Apologies if any offence caused. Probably a poor choice of words. Point does stand though, although I didn’t really want to get into an argument by being specific but seems as though I’ll probably have to. Again no offence intended. A switch itself is very unlikely, if not impossible to cause nuisance tripping. Will be a waste of effort swapping them. Only if there was a fault between the switch and an earthed back box could it cause tripping. Loose connections won’t cause tripping. More likely flickering lights etc or even a fire. Going round randomly tightening connections will be a waste of time - unless you have AFDD’s fitted, but this is unlikely as they’re not in widespread use here yet. Although it’s very debatable whether they actually work on lighting circuits as the current is too low. Note that AFCI is an American term for the same thing. Would be handy to know if it’s an MCB or an RCCB or an RCBO where the problem is. Unlikely to be an earth leakage breaker, these are mostly obsolete and came before RCD’s (RCCB/RCBO’s), some of which are current operated (basically an RCD) and some of which are voltage operated (on the earth). These are not really safe for use. PVC insulation won’t deteriorate in 20 years unless subjected to very high loads or extreme temperatures etc. If in a domestic property it’s unknown how long it will last in good conditions as the earliest examples from the 60’s are still in good condition. Fuses/fuse wire very seldom blow through age in my experience, although it does happen. Very normal to change an old fuse board from 40+ years ago that appears to have most of the original fuse wire intact. Usually the lighting circuits that go when incandescent bulbs/lamps blew. Or the odd ring final circuit where they’d had a dodgy appliance perhaps. Cooker and immersion circuits the least likely to go in my experience. Also, I’m not sure it’s a good thing if you’ve got fuses that don’t disconnect in the event of a fault and just battle through!!

It does sound like it’s probably rodent damage. Especially if you can hear them! Should be straightforward for an electrician to locate with an insulation resistance test. Hopefully if access to cables in loft is ok it might be a simple fix too. The only thing you could try is to turn off the lighting circuit and get up there an expose the wiring and inspect for damage. Turn it off first though! I’ve seen it plenty of times where rodents have stripped cables bare! You probably need to ignore most of the well meaning advice on here as half of it is nonsense in this instance. Getting a good electrician to sort is going to be the easiest and quickest fix here

With that much work it’s going to be cheaper and better to knock it down and start again, doing it properly.

Looks like 10mm2 T&E most likely to me. Gut feeling is it’s not 16mm2. No such thing as 80/64 amp cable. Depends on reference method, type of load, length of run and de rating factors. 10mm2 is 64 amps in absolute perfect conditions. Unless I could inspect every inch of the run and was happy, I personally wouldn’t be wanting to go over 50 amps OCPD as a rule. Either way, almost certainly that cable isn’t safely supplying 80 amps to the other end of your house.

Don’t see why not if on different MPPT’s

Does grid voltage dropping always correlate with the higher load as per the graph in OP? If so I’m going to guess at a high resistance joint somewhere. Could be in your installation (consumer unit main switch maybe), or in DNO’s