Gate valve fitted in boiler return from megaflo

[Lower]

We've not long been in possession of our new house and i'm trying to get my head round some of the plumbing.

The heating system is only a couple of years old and seems quite noisy. I'm used to a virtually silent system but there is some definite pump noise that you can hear in the rooms adjacent to the airing cupboard where the megaflo and heating system pump are located.

The first thing i noticed is that there is a gate valve fitted in the return to the boiler from the megaflo coil. The valve seems to be about half open.

Any reason why this should be there and why it shouldn't be fully open? I can find no reference to the requirement for a gate valve in the megaflo fitting instructions and can only assume its been fitted to slow down the water flow through the megaflo.

 

[Agile]

Oh dear! Its better not to touch things if you dont understand them.

A quick search on this forum would find they are usually mentioned at least once a week.

Its to balance the flow through the cylinder, partly to set the differential to about 10-15 c if its condensing, and partly to set to give adequate flow round the heating when the HW is also being heated.

Tony Glazier

 

[Lower]

Thanks for your response.

I thought it might be for something like that but didn't even consider doing a search.

Just as well i carefully counted the number of turns to fully open and then put it back where it was!

 

[Agile]

That was very sensible!

However, usually they are not correctly set and are too far open. Usually the adjustment is at around just one turn open. But there is considerable hysteresis and any reference should be when opened from fully closed and the adjustment always made in the opening direction. You can lose half a turn in the hysteresis.

You can adjust them pretty adequately just by feeling the temperatures of the flow and return to the heating coil. But they do take about 4-5 minutes to stabilise after any adjustment which should be very small, say 1/4 turn or less.

Feel the temperature difference, it should be definately noticeable but not excessive. I used to teach trainees to judge by how many seconds they could hold a pipe for.

You need to check and set with the cylinder mostly cold and heating off.

Then to recheck with the heating on but all rads warmed up and the water on as above. The differential will increase as there is less pump pressure to create the flow.

Of course all these settings are approximate and affected by the relative temperatures, TRVs on rads and any auto bypass valve opening.

Tony

 

[Lower]

Thanks Tony, I will check it's position using the method you describe.

It was certainly much more than 1 turn open.

I've also noticed it takes quite a while for the radiators around the house (generally, not limited to the furthest away) to warm up properly when the hot water is on so it would make sense if this valve is too open and too much flow through the megaflo.

Now on to my next question