boiler feed and vent pipes

[mjd]

System details:- condensing boiler with fully pumped Heating & H/W open vented

Due to proposed building works at home I want to move the hot water cylinder from upstairs, to downstairs next to the boiler, but to save work I would like to move the existing cold feed and the open vent from the flow pipe to the return pipe. If I do this will it cause me any problems? I cannot see why it should but then I not an expert.

Thanks for any help

Mike

 

[felix]

If your vent is going to function as a vent you MUST have an uphill path from the top of the boiler's heat exchanger all the way to the open end. Putting it in the return pipe is no good because your boiler will keep filling up with air or, if its thermostats fail, steam! This is NOT GOOD. Note that if the pump is in the flow side above the boiler this will run dry too.

Since this is a fully pumped system, the vent and feed MUST join onto the same piece of pipe very close together. If you ignore this rule you risk joining the ranks of distraught people on this forum with water gushing from their vent pipes.

The simple answer to your question is therefore no. Remember that since your vent will no longer be at the top of the cylinder heating coil you'll have to put a bleed valve on there instead. Put it on a 'stalk' so that air has somewhere to collect until you get around to bleeding it.

PS: If you have a choice, the best place for the pump is in the return pipe where the water is a bit cooler. A typical layout goes boiler - feed/vent - zone/diverter valve(s) - cylinder/rads - pump - boiler.

PPS: Here's another pitfall to avoid. If you have more than one return pipe from your radiators, make sure they all converge into a single pipe BEFORE the HW return pipe joins in. I once had a professionally installed system in which the radiators heated up when only HW was on. It wasn't a faulty valve. It was water from the cylinder coil shooting straight into a rad return pipe. From there it went BACKWARDS round one rad circuit, came up against the closed valve and finally returned to the boiler in the correct direction around the other circuit. The pipework was so convoluted I cut the whole lot out and started again.

 

[kevplumb]

PS: If you have a choice, the best place for the pump is in the return pipe where the water is a bit cooler. A typical layout goes boiler - feed/vent - zone/diverter valve(s) - cylinder/rads - pump - boiler.

never seen one done like that

 

[brumylad]

Oh dear not the pump on return V's pump on flow argumant again. This will surely carry on until everything goes electric underfoor heating.

 

[kevplumb]

and the last time you came across a fully pumped with the pump on the return
WAS

 

[doitall]

and the last time you came across a fully pumped with the pump on the return
WAS

never seen one yet

 

[ollski]

Must confess I have never heard any argument for deliberately putting the pump in the return......putting negative pressure on the majority of the system can't be a good thing can it?

 

[htgeng]

Must confess I have never heard any argument for deliberately putting the pump in the return......putting negative pressure on the majority of the system can't be a good thing can it?

Many boilers with built in pumps have the pump on the return.. or am i missing something here?

 

[felix]

putting negative pressure on the majority of the system can't be a good thing can it

OK, I'll concede that one. I've learnt to bleed upstairs radiators only with the pump off. It's no great hardship but it would confuse the hell out of anybody who didn't realize what was going on.

"I opened the bleed valve and I swear it was sucking air IN. Help!!!"

The nice plumber who fitted that convoluted mess put the pump in the return pipe "because the water's cooler and your pump will last longer". It was one of the few bits he actually fitted well so I left it.

 

[DP]

Feed and vent connections also incorrect. Should be Vent and then feed.

 

[mjd]

Thanks for all your help, looks like i got to run yet more pipes.


Mike

 

[bripl]

pump on the return is common practice although not good practice.most sys boilers plus combis are on the return.open vented sys close coupled pump on the flow is thenorm

 

[felix]

Feed and vent connections also incorrect. Should be Vent and then feed.

Well spotted DP. A slip of the keyboard there.

Mjd, the vent pipe should be nearest the boiler with the feed immediately afterwards. That way, air bubbles making there way along the flow pipe come to the vent first instead of bubbling up through the tank.

On reflection I can also see a slight overall advantage in putting the pump on the flow side of the boiler - but mine is staying where it is!

 

[doitall]

On a fully pumped system with the pump on the return, the cold feed and vent has to connect at the boiler.

It cannot tee in behind the pump in the normal way.