No bypass valve...

[conoral11]

I've got a gravity feed y-plan CH and DW system that has had some radiators fitted. Its got a combined feed and vent.

I've had x400 in the system for the past 3 weeks, and have drain and flushed it all out, was nice and clean.

All radiators other than the towel rail and the one in the room with the room thermostat have TRVs.

When the CH turns on, you can her the glug of "I've still got air in me", before the system then settles down.

If I run just the DW I get the same effect, however after 10-15 minutes there is a lot of gurgling going on, unlike when just the CH is on.

The towel radiator turns on with either CH or DW so I assume it is connected to the primaries. I have to bleed this radiator when ever the DW has been on.

During my investigations, I've noticed that there is a 15mm pipe teed off from between the pump and the mid-point valve. This then goes down into the wall (All of my useful to know pipes go into the wall...) where I am assuming it joins the return.

I'm assuming this is a bypass line, that really should have a valve(Manual or auto) but doesn't.

Would I be correct in assuming because this pipe bypasses the system, I'm more likely to have difficulty getting out any air locks in the system? Should I add a valve here to aid me with bleeding the system?

Best Wishes

 

[flameport]

a 15mm pipe teed off from between the pump and the mid-point valve. This then goes down into the wall

More likely to be what feeds the towel rail, which is probably intended as the bypass. You don't need another bypass valve, but the towel rail valve(s) should be set to only allow a small flow.

Having to bleed continually means air is getting in somewhere - you need to find out where.
Unless the air is a product of corrosion, in which case the 'air' will burn when a flame is applied.

 

[conoral11]

flameport,

Thank you for the reply.

I first thought that air may have been getting into the system through the open vent, hence the now combined feed and vent. That made no difference.

What is rather odd, is if i put the pump on full speed (Grundflos usps-2) I don't seem to get this issue, although it may be that the pump is breaking up the air a little so we don't notice the gurgling. I still need to bleed it however.

The pump is new, and there is an auto bleed valve after the midpoint valve on the hot water cylinder side, and another on the old cold feed vertical pipe in the loft.

Are there any other obvious places that air may be getting in that I've over looked? I've tried the fast then slow speed pump settings to 'rock' any air that I can out, with little success.

Best Wishes

 

[flameport]

and another on the old cold feed vertical pipe in the loft.

Not impossible that air is being drawn in that or the other one, the feed should be on the suction side of the pump.
Close the screw on the top of the auto bleed valves, or stretch clingfilm or similar over them and tape in place.
An open vent system shouldn't need them anyway.

 

[conoral11]

Taking a further look at the system,

If I run the central heating, with just the bypass rad on, turned low but not off, we get significant gurgling in the pipework, and finally steam out of the combined cold feed and vent pipe.

I took a contact temperature probe and measured the pipes coming from my Potterton Suprima 30l boiler. The left pipe if 5c below the right pipe... however looking at the installation manual suggests this is wrong and that what I am seeing is the flow and return crossed on the boiler.

The left pipe should be the flow, and the right should be the return.

The pump is correctly connected in the system, pushing water towards the mid-port valve.

Is my assumption correct? And could this be the cause of my hot water circuit gurgling?

 

[rochdalegas]

Was it ok before you fitted the new pump?. Double check its fitted the right way round if not.

 

[rochdalegas]

Reread and edited

 

[conoral11]

Having checked the pump, it is indeed the correct way round, pushing water towards the mid point valve. As far as I know, the system has always had "issues" and all the thermostats, hot water and room have usually been only a very low temperature before we moved in. I am suspecting this was so that they would switch off before the system started over heating.

Done another test today measuring the temperatures from the boiler pipes and the right side (Supposed to be return) is anywhere between 5-9c above the left pipe.

The pump was replaced because it was originally thought to be at fault. On removal the pump was in very bad condition, most of the windings had become damaged.