System pumping over

[Millsy 82]

I have a bit of an odd job I have got a system that only pumps over when htg/dhw on together but if I run them seperatly it stops.

The custard has replaced the pump about a week ago then when his heating didnt work called me in found a blocked cold feed. Filled it back up tested it a non return valve started vibrating under the floor where htg tees into boiler return. Swapped that and it is now pumping over I dont know whether it used to before they fitted the new pump but its doing it now and I get the fun job of sorting it.

Now the only things I can think are

1 Sludged up causing too much pressure. Water came out clear but then the cold feed was blocked solid.

2 Piped up incorrect (thats why the non return valve is there) they had an extension built so I am kind of guessing they tagged the new rads into the return and they started to get hot with dhw so they put this in. Cold feed and vent piped up correctly.

3 Not enough head above the pump about 1mtr above pump.

Its been ages since I have had this problem and my brain has gone blank.

 

[diamondgas]

Can you combine the f&v Millsy 82? Easiest way to overcome pumping over IMHO

 

[Millsy 82]

Never done that before. I was always taught to pipe them separate to stop air from being sucked in.

It would be a bit tricky but possible where abouts do you join them near the tank outlet or nearer the boiler flow

 

[diamondgas]

Cap the 15mm feed near the pump, change the header cold feed connection to 22mm and join it straight onto the vent pipe. No need for the loop over the top! You MUST check that the appliance is suitable for this. They will have an overheat device fitted and are usually suitable for sealed systems ... what boiler's fitted?

 

[Millsy 82]

Glowworm Micron.

I just think its odd that it on pumps over when both htg/dhw are on together I think when they did the extension they bodged it in and with an old pump it never happened before but now they have a new pump its showing all the problems.

 

[diamondgas]

Glowworm Micron.

I just think its odd that it on pumps over when both htg/dhw are on together I think when they did the extension they bodged it in and with an old pump it never happened before but now they have a new pump its showing all the problems.

Does sound like there's a pipework configuration amiss somewhere for sure! Low head configurations aren't the best The mi's state that the boiler has an o/heat and can be fitted on sealed system. It also gives recommendations for vent height etc... That's normally where the issue lies, especially with low head systems! Personally I wouldn't look to deeply into it. May be worth checking with the manufacturer's regards a combined f&v but all the safety aspects are there to say it can be combined IMO

 

[Millsy 82]

I'll give them a bell tomorrow.

 

[diamondgas]

I'll give them a bell tomorrow.

The only issue when combining the f&v is that there's the provision to shut the appliance down before it reaches boiling point; the system is still open and expansion is still accommodated via the header