Is my pump backwards?

[molgrips]

what is the boiler pressure when hot?

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.

 

[Agile]

Traditionally, the pump was always put on the return to the boiler as the lower return temperature should give a longer pump life!

 

[gas112]

Traditionally, the pump was always put on the return to the boiler as the lower return temperature should give a longer pump life!

pump was on the return when it was gravity systems and completely differently configured

 

[molgrips]

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 running for a bit, and C and D are quite warm. The pipe between the ABV and the pump is now quite hot. I thought it may be conduction making it warm but the pipe through the HW motorised valve , which is the same distance from the pump is pretty cool even behind its insulation, so it can't be that. My concern is that something is leaking heat into the return flow and reducing my condensing effect. That could also explain how the delta T is so low at the boiler.

It's as if the ABV is leaking. I have just replaced it with a brand new one, although it was cheap (that's all that was available) and I have set it to open if I turn both motorized valves off by hand. So it should not be opening, unless it's just leaking because it's cheap and a bit crap?

 

[Johntheo5]

What is the ABV set to??.

How do you turn off the motorized valves by hand?.

 

[molgrips]

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

 

[Johntheo5]

If the ABV index is anyway accurate and represents 0.2bar or 2M then set far too low IMO, with the CH or the DHW M.valve only open is it still passing, ABV inlet+outlet hot?, if so just keep closing it gradually until the pipes get cold.

 

[molgrips]

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 water was flowing the other way through the system...