Isolation Valves on Flow and Return Pipes??

[scott2hot]

I've been asked to extend a central heating system, adding a small towel rail and a small rad for a kitchen. The flow and return pipes I plan to extend from (15mm) have standard isolation valves fitted on them. The dilema I have is whether there will be sufficient flow to feed these two new additions. The pipes currently are currently supplying just a single rad, I'm worried that due to the reduced bore of the isolation valves there will not be sufficient flow for the addition. Do I drain down and remove the valves or simply isolate and extend the system and then repressurize the system. The system is a Valliant Combi Boiler.

Many thanks

 

[dontknowitall]

Radiators should really be fed from the main flow/return pipes as opposed to extending from existing radiator feeds.

Sometimes you can get away with it but more often than not you will find the customer complaining that one of the radiators is not warming enough and then you'll end up having to redo the job and make a loss on it as you won't be able to charge the second time around.

In answer to the question on the bore, it shouldn't affect the flow too much to make a difference but this will depend on the pump, the pipe runs and so on. Much better to drain and make a proper job in my opinion.

 

[Billy Bob Bob]

you could alternatively fit full bore quality iso valves rated to 10 bar so they dont burst

 

[WHPES]

Remove the isolation valves. They should not be used on a heating system. In time they will only leak anyway. The only valve suitable to use on heating is a gate valve which I would not use. Drain everything off, remove and do your plumbing, then fill back up and add fresh inhibitor.

 

[capitanpugwash]

Is a gate valve suitable on a pressurised system? I thought not?

Surely on a zoned system with say 3-4 zones in a large house it would be wise to have an isolation valve on each return (with the motorised valves on the flow) to allow work to be carried out on one zone without draining the whole system?

Something like this: http://www.*************/p/full-bore-lever-ball-valve-22mm/30584. Where you have to replace the middle with scre wfix. Surely they're good for the job?

 

[unguided1]

I see gate valves all the time on unvented system and I personaly do not like to see it.

I would say drain down the system and do the job properly after that will be what the customer is asking for and will be paying you for.

Ordinary ballofix valves are to restrictive any way, thats why theyre called isolation valves

 

[SimonG]

Is a gate valve suitable on a pressurised system? I thought not?

Surely on a zoned system with say 3-4 zones in a large house it would be wise to have an isolation valve on each return (with the motorised valves on the flow) to allow work to be carried out on one zone without draining the whole system?

Something like this: http://www.*************/p/full-bore-lever-ball-valve-22mm/30584. Where you have to replace the middle with scre wfix. Surely they're good for the job?

Use gate valves all the time. Tend to install lots of s plan systems and always fit extra gate valve after 2 port valve so that you can close pump gate valve, close the gate valve after 2 port and change 2 port valve without draining down. Also fit gate valve on each zones return for the reason stated above. Particularly good for changing rad valves, close both valves release the head of water and change a rad valve in a couple of minutes.

 

[WHPES]

Whenever I come across ball valves on a central heating system such as isolation valves they are always leaking from the middle.

 

[SimonG]

Whenever I come across ball valves on a central heating system such as isolation valves they are always leaking from the middle.

and if by some chance they are dry, they're not as soon as you have to touch them!!

 

[Billy Bob Bob]

you could alternatively fit full bore quality iso valves rated to 10 bar so they dont burst

i was talking about lever full bore ballofix, cheapies (not original ballofix)will leak from the centre guaranteed

 

[heatybob]

remove the valves they will restrict the no doubt(a 15mm ballofix will reduce the flow to equivalent of 8-10 mm tube) imo if the rads are as you say size wise you will have no problems connecting them (with valves removed)imo!!!!!.A general rule of thumb i use and have for many years on both copper and steel htg runs is 22mm(3/4) reducing to 15mm(1/2) for last 2 rads on run especialy on sealed systems,hope this helps

 

[dm65]

Aha - I'm not a plumber like you guys and when I cut back some pipe to change a radiator & reposition, I fitted isolators and left them in place when I reattached everything and I'm getting drips from the middle

One more lesson learnt and they will be binned at the weekend thanks to this thread

Regards

Denis

 

[doitmyself]

I've been asked to extend a central heating system, adding a small towel rail and a small rad for a kitchen. The flow and return pipes I plan to extend from (15mm) have standard isolation valves fitted on them. ... The pipes currently are currently supplying just a single rad,

Provided the total kW (existing rad plus new items) down the 15mm pipe does not exceed 6.5kW, there should be no problem.

 

[happyflyer]

Doitmyself,


That's providing the flow for 6.5kws in that 15mm is available and not going somewhere else, I think it will perhaps need a bit
of balancing don't you?

 

[Ermintrude]

Isolation valves turn that 15mm into 8mm at best plus they leak. Remove them.

 

[doitmyself]

That's providing the flow for 6.5kws in that 15mm is available and not going somewhere else, I think it will perhaps need a bit of balancing don't you?

The OP was concerned that the existing 15mm pipe wouild not be large enough for the additional rad and towel rail. I was just pointing out that 15mm can carry up to 6.5kW.

Of course a system will need rebalancing if extra radiators are added.

Wait for the sequel: "I've added a rad and towel rail to my system and they don't get hot. What have I done wrong?"

 

[stevetheplumber]

its not so much the type of valve you use its the quality of the valves you use i know systems with gate valves on that are 20 plus years old valves work fine for what they were intended and dont leak including ballofix valves
if you pay 49 p for an iso valve from screwfix it is what it is a temporary stopend

 

[kris]

Old thread revival.
Just remember Dennis that some of the isos are directional if putting on heating pipes.

 

[AWheating]

most cheap iso valves are only rated to 65 degrees (hot and cold water), you need higher rated valves designed for use on heating systems. gate valves are fine with or with the wheel.