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The pipe just after the ABV stays cold for a while, but C and D always warm up slowly. It's a mystery I don't think I'll be able to solve. The heating is working well anyway so I can just leave it like that. The thing nagging at my mind is why the boiler's delta T was much greater when the...

On mine the motor unit is attached by a magnet so you can pull the motor off and turn the tab underneath. ABV was set to 0.2

I tried the experiment. With a cold system I blocked off the upstairs rads, ran the system and C and D were cold. When the flow got warm I opened up the upstairs rads; they got hot but the pipes very slowly became lukewarm. So my theory appears not to be true. However, now the system has been...

About 1.3 bar because it's on the lower pressure side of the pump.. There is still plenty of air in the expansion vessel - I made sure of it, so it's still working fine.

Yes.. of course... I'll try that when it cools down. A should be the flow, shouldn't it? I can also test my theory, I think, by closing all the rads on the top floor. If pipe D stays cold, and then gets warm quickly when I fully open a rad, then I'll know. Ideal ICOS HE 12. I know which...

There's no way of knowing. It goes down through two floors, and not straight down either it dog-legs under the floor. I'm comfortable, but I'd be more comfortable with a lower gas bill! I mean it's not high but it could always be lower. I think I have worked out what the extra mystery pipe...

So it's the right way round? Why is dT so much greater if the flow is reversed? Is dT of 10C a problem?

It's what's in my cupboard!

I posted a thread a while ago about strange boiler temperature behaviour in my S-plan heating and hot water tank system, and I concluded that water was flowing through my boiler backwards. This was definitely the case, however I wasn't sure if the pump was simply backwards or the boiler pipes...

Update: I flipped the pump around - easy enough except that I didn't have any replacement rubber washers. The old ones were quite knackered so I greased them up and refitted anyway, and they somehow haven't leaked! The temperature controls now work as expected - you can set the flow temp to...

Looks like the pump. They've installed it with the writing the right way up but the flow arrow pointing down. It has two isolating valves either side and two big screw connectors. I can shut the valves, release the pressure via the bleed screw and turn it round, I don't even have to release the...

I think my pump has been installed the wrong way round. Looking at the boiler manual the pipe on the right should be the outward flow and obviously hotter. But it's the colder of the two. This would explain my symptoms as the boiler is trying to modulate the return flow! And maybe also why...

Cautious yes. I paid £250k for this house I don't want to destroy it! Can you imagine? Block and beam makes sense..the garage floor is one piece of concrete so I'd thought the whole floor was. But thinking about it, it would be incredibly hard to pour a suspended concrete floor!

My house was built in 2007 in an estate on a sloping house. The floor is concrete but there's space under it as you can hear it resonate when you stamp on it. We watched the other houses being built and we know many of them have a full room sized void underneath, but we don't know if we have...

No, it takes a good while. It was probably on for 10 mins and off for 10 mins although I didn't time it. There might be short cycling protection giving minimum burn/off times of 10 mins, I suppose, which would produce these symptoms. The pump is a Range Tribune, I've got the flow set to low...

With the temperature knob on the second pip, and all rads open but no HW, the burner turns off at 57C and back on at 38C. So that's 19C differential which means it's 8.5C either side of set point. That's probably acceptable for the heating. The return temps stay low, around 48C, and the house...

Yeah a bit tricky when it's not that cold yet! I may have to continue my investigation when it's colder and open all the windows first. Or, just run a bath and use the hot water cylinder to take the load. But I'm not sure how much heat my hot water coil can dump.

Yeah I just tested it and these are definitely K. I readusted my thermocouples on the pipes, no change. I removed the control panel and tested the potentiometer - fine. I might have to get a refurbed replacement PCB off eBay they are only £30.

Yeah I'll do this tomorrow. I tried it with just the non-TRV rads on and the dial set even lower, still went up to 65C or something. It's definitely not working properly - either that or my thermometer. If I select type E thermocouples on my thermometer instead of type K the numbers look...

There are 6 pips on the temperature control knob, and the manual says it goes from 30 to 80C. So logically, each pip should be 10C and I've attached a picture of where I had it set which should be 50C. So I fired up the hot water and watched the temperature control. It throttled back...