Weirdness in flow and return temperatures

Mekrel · 3 Dec 2024 at 19:01

I've been trying to ensure our heating system is working efficiently, namely due to not knowing how well it has been setup prior to moving in and I've had new TRV and lock shield valves installed downstairs whilst we had the radiators off for decorating. A few of the old TRVs wouldn't close, and some heads were keeping the pin pushed down despite being on the highest setting.

I think I've balanced the system pretty well, I took starting temps centre top of each rad before turning the heating on and took a new measurement every 5 mins to see which heated up the fastest (using a handheld IR camera). Then in sequence I've adjusted the lock shield valves and they're heating up evenly and there's a 10-12° difference between inlet and outlet pipe.

What I have noticed though is the return to the boiler seems to be hotter than the flow? The boiler is an oil fired Grant Eco Vortex, so I'm looking for a 20° delta flow and return, with the flow being less than 55° so it condenses. No digital display on the boiler to set the flow rates, just an unmarked dial...

The flow and returns are marked with a paper ring, which is where I'm taking the IR readings from as it's difficult getting a reading from copper.

The only thing I'm thinking is the pump setup? It's a Grundfos UPS3 and has been set to constant speed setting #3, but it seems to recommended setup for two pipe heating systems is proportional pressure setting #2. I think it's a two pipe system which is what proportional pressure setting is recommended for.

Any ideas why return could be hotter than flow? I've heard without the pump running heat can creep back up into the return but I've measured during the system running. Not sure how accurate the IR is taking the reading from the paper rings. I do have a thermocouple thermometer on its way to me to double check.

Coran · 7 Dec 2024 at 14:38

The obvious answer is that the flow and return have been labelled incorrectly.

Unless there’s an additional heat source that the system is passing through, the return can’t be higher (e.g. a tank with an immersion heater on). Presumably both pipes you’re measuring are above room temperature, so must be losing heat and not gaining.

Mekrel · 7 Dec 2024 at 18:37

I'm starting to think that's the case, although the install manual for the boiler has the return at the top. So I'm starting to think the return is actually going up to pump in the airing cupboard?

Manual:

danlightbulb · 7 Dec 2024 at 19:48

Turn the heating on from cold and you'll soon see which pipe is the flow.

SpellowHouse · 7 Dec 2024 at 19:55

Usually the flow is on the top. Also, another way to tell is that the pump is usually on the return.

In general, it may be that the pump is in the wrong mode. Plumbers have a habit of just turning them to manual III, which is rarely correct. It's just the "safe setting" when you want to get the job done and go home.

Mekrel · 7 Dec 2024 at 20:12

The top is 100% the flow, it's just strange that the install manual says for the return to be at the top.

The pump was on constant speed III, I've set that to proportional pressure II as that seems to be the recommended setting for dual pipe setups.

The pump is on the flow, looks like the flow pipe comes up into the airing cupboard, through to the pump, Ts into motorised valves for hot water and central heating.

Just seems strange the manual stipulates a certain setup. We've been in a year so I need to get someone to come out and service it anyway so I'll get their opinion.

SpellowHouse · 7 Dec 2024 at 20:29

The flow of the pump is marked on the base, on the side. It's not dependant on the orientation of the top. There are four Allen key bolts that connect the top to the bottom. Undo those and you can rotate the head without changing the flow. That's a very long way of saying you could actually have the controls the right way up instead of upside down, lol.

They were traditionally placed on the return because of the lower temperatures, extended the life of the pump. However, it's only a guide.

Mekrel · 7 Dec 2024 at 20:39

Yeah the arrow is pointing down so the pipe marked as the return is actually on the negative pressure side of the pump, so it's actually the flow. I'm guessing there's supposed to be temperature sensors in the boiler so the flow sensor is actually going to be reading the return temperatures.