Replacing Gate Valve with Auto Bypasss Valve

[JayTee]

Could someone advise please?

Our Heating system is open vented with an indirect hot water cylinder. The boiler is a Glow Worm Ultracom 30 HXi and the pump is a Grundfoss UPS 15/50. The radiator pipework is 10mm microbore and there are TRV's all but one radiator.

Currently there is a 15mm gate valve between the flow and return, after the pump and before the 3 way valve. I asked the plumber that installed the boiler whether an auto bypass valve should be fitted instead but he said it was fine as it is. However having since read the boiler manual it states that an auto valve should be fitted. To my mind this would also help the system heat up faster and be more efficient as all the water from the boiler is sent to the rads when they initially warm up before the TRV's close instead of the current valve that is always slightly open - Is this the case?

Can the auto valve just be fitted in place of the current gate valve?

Thanks

 

[45yearsagasman]

Yes, simply replace the old gate valve and fit auto bypass. You may have to alter pipework. With a 3 port valve and one rad with no TRV it is usually not necessary for a bypass at all.(There is always one port open if it is a mid position valve) Try closing the bypass and see how the system performs.

 

[JayTee]

Ah I see, so with the heating on, hot water off and all the TRV's have closed there will be enough flow through the one rad with no TRV to avoid any damage to the pump and system? Or the other way round with heating off and hot water on only?


Altering the pipe work should not be a problem, are there any specific specs for auto bypass valve pipe routes in terms of length or proximity to bends. Or just enough room to fit the valve?

 

[45yearsagasman]

The main consideration when heating on and all trv's are closing down is that the correct flow rate is maintained across your boiler and for that I would go ahead and fit the auto bypass.

 

[doitall]

I would fit the ABV as well especially since the rads are on 10mm.

 

[JayTee]

Ok thanks for the advice chaps. Having looked at the prices it seems to be a lot cheaper to get a 22mm valve and reduce it down to 15mm...

 

[doitall]

Not a problem doing that.

 

[Agile]

Unless you live in a six bedroom house your boiler seems oversized. So there is plenty of power to heat the system.

Having an always open valve can slow heatup because the return heats up faster and the boiler modulates back.

Because you have microbore you should certainly fit an ABV as a single rad is unlikely to provide the minimum flow the boiler requires.

The ABV needs to be set up to just start to open when 25% of the rads are turned off.

Tony Glazier

 

[JayTee]

Unfortunately we do not live in a 6 bed house The plumber that supplied and fitted it said at the time there were non of the correct size available and would do the larger one for the same price. I guess it is probably not quite as efficient as using the correct size boiler for the system though...

 

[JayTee]

The ABV needs to be set up to just start to open when 25% of the rads are turned off.

Tony Glazier

Ok, fitted auto bypass valve and all seems ok. When I came to set the pressure it opens at as per your suggestion above I found that even wound right down it still seems to let some water through as the pipe is getting hot on the other side of the valve straight away, whereas I was expecting it to stay cool until the valve opened. Do they let a small amount of water through no matter what the setting or do you think the valve is faulty...

Cheers...

 

[Agile]

Unfortunately we do not live in a 6 bed house The plumber that supplied and fitted it said at the time there were non of the correct size available and would do the larger one for the same price. I guess it is probably not quite as efficient as using the correct size boiler for the system though...

I find 12 kW, 15 kW, 18 kW and 24 kW models available and priced from £575 to £700. Those prices may not include VAT or the flue.

Its particularly important with smaller systems to have a boiler matched to the system so that it can modulate back.

Its not normal for ABVs to leak unless there is dirt on the seat. A small amount of leakage will not matter much.

With microbore the pump pressure could easily be 4m or higher!

Tony