Does a Closed Central Heating system need a Bypass Valve open?

[Mtbamplumb]

HI All,

Quick question, had problems with our central heating system, with some radiators not heating up properly.
Finally mapped it all out and found that hotel water come from the boiler and through the pump, then there are 3 options:
1) Branch off Through Central Heating control valve to the radiators.
2) Branch off through a manual bypass valve back to the boiler return.
3) Through Hot Water control valve to the hot water tank and then out to the boiler return.

Originally the bypass valve was wide open. I closed this and all of a sudden, problem radiators began heating up immediately.

My question is, can the bypass Valve be closed permanently? or is there a reason this should be open?


thanks for your help.

 

[oil gasman]

if I understand u correctly u have 2 x seperate motorised valves or 2 ports

may I ask what boiler have u got , if u have pump over run on your boiler the bypass is required and not to be fully closed as when both motorised valves close and the pump carries on running it needs to go somewhere , so that's what the bypass is for

have u got trvs fitted on every radiator

u may be better of with an automatic bypass

the bypass must be after the pump and before ur motorised valves and it sounds as though it is by ur description

is is there a valve on your hot water cylinder return pipe

sounds like your system needs balancing ,

water er will always find the easiest route round a system , if u close the bypass valve just a little bit it will push heat else where , thus that why ur rads started to get warm

hope that helps abit

if it does need balancing and u can't somehow balance it correctly get a gsr heating engineer in to sort it out and also fit an automatic bypass for you and give your system a once over inc the boiler to ensure its all safe and for your peace of mind

 

[Mtbamplumb]

hi Oil Gasman, thanks for your quick reply.
yes there are 2 seperate motorised valves.
Boiler is a Glow Worm 30Hxi
Have TRV's on all but 2 Radiators which have lock shields on both sides that are open.
have had persistent problems with 4 rads on same loop until i closed the bypass.
Valve is after pump but before both motorised valves as you have said.
Bypass valve was full open, if i open it slightly, will this be enough to give it enough flow so that when both the Central heating and Hot Water valves are shut it will work?
I believe there is an over-run as when i switched off the CH and HW, the pump continued to run for about 3-5 min.

When i did this even with the bypass closed, pressure remained unchanged, does this mean that it is ok to leave it closed?

As for an Automatic Bypass valve, are these fairly standard to fit?

thanks for your help.

 

[oil gasman]

happy to help

the bypass must be left open, u don't have to leave it fully open you can close it down a few turns

if the bypass is 22 mm and with the valve fully open it will find the easiest route and can bypass some radiators completely if they are the furthest away

the heating circuit is just one big loop and the heat needs to reach the furthest one from the pump

the pump isn't actually a pump, but circulates the water , but virtually everyone calls it a pump , but thats neither here or there

if the valve is closed the pump with deadhead , in other word will be like a car going down a deadend street knowhere to go , It can cause a boiler to go to hard overheat lockout, where u would then have to get a gsr engineer in to reset the boiler inside

an automatic bypass works that when both zone valves closes the water is being pushed and wants to go somewhere , so the auto bypass open as much as it needs to , allowing water to go through the bypass and keep the pump from prematurely failing and stopping the boiler going to overheat

if u close the gate valve which normally has a red wheel on it , then open it 3 turns , see how u get on

by adjusting it bit by bit, but must not ever be fully closed due to the pump over run and possible overheat

the autobypass are standard fittings and I always useto fit them instead on manual ones for this very reason , so it would push the maximum amount of neat to the rads and cyl where needed but also opening when the overun came in


on the hot water cylinder return pipe, should be the bottom one u should have another valve, u can close that a little bit , will help to push heat towards the heating when both the hw and ch are on at the same time

if u get a gsr engineer in to fit a auto bypass for u , ensure he puts a system protector in ,

hope that helps abit

 

[chris watkins]

http://www.glow-worm.co.uk/glow-worm/hxi-range-157210.pdf

Your condensing boiler requires a Auto By-pass (page 18), in fact when it was installed it would have been a legal requirement under the Building Regs AD Part L that the manual one be replaced with an automatic one otherwise the boiler will not work as efficiently as it should.
Wonder why it wasn't ? has the boiler been in long?

I don't agree with oil gasman about the balancing valve on the cylinder return if it is a newish cylinder, but otherwise as he said get a auto one fitted & set up.

PS a by-pass is also required as you have TRVs fitted to guarantee a minimum flow rate through your boiler it requires min of 1220 L/H (20.333L/m)

 

[oil gasman]

sorry double posted

 

[oil gasman]

http://www.glow-worm.co.uk/glow-worm/hxi-range-157210.pdf

Your condensing boiler requires a Auto By-pass (page 18), in fact when it was installed it would have been a legal requirement under the Building Regs AD Part L that the manual one be replaced with an automatic one otherwise the boiler will not work as efficiently as it should.
Wonder why it wasn't ? has the boiler been in long?

I don't agree with oil gasman about the balancing valve on the cylinder return if it is a newish cylinder, but otherwise as he said get a auto one fitted & set up.

PS a by-pass is also required as you have TRVs fitted to guarantee a minimum flow rate through your boiler it requires min of 1220 L/H (20.333L/m)

thats why I always fitted an automatic bypass as part of building regs , however u often came up where one hadnt been fitted by another company

ref the cylinder, I always put a gate valve on the cylinder return , as an aid for balancing , also helps when flushing the system

even on quick recovery cylinders found cylinders without a gate on can rob the ch side and always fitted one in order i can balance the system up correctly , otherwise it would act as a massive bypass and rob the ch side when on

was always taught that for many years but maybe things are done differently now, but going from experiance in being able to balance the system

chris , hope u don't think I'm being rude but was always taught that and also fitted one from experiance with regards to fitting a full bore gate valve onto the cylinder return otherwise it would be difficult to balance the system

 

[Mike Jackson]

last time I did unvented I was told that a balancing valve shouldn't be fitted to cylinders now to comply with part L. As all systems should now have full control of heating and hot water best practice is to set the water to come on earlier than the heating so that the cylinder takes the full heat output of the boiler, by the time the heating comes on the cylinder will be up to temp.

 

[oil gasman]

last time I did unvented I was told that a balancing valve shouldn't be fitted to cylinders now to comply with part L. As all systems should now have full control of heating and hot water best practice is to set the water to come on earlier than the heating so that the cylinder takes the full heat output of the boiler, by the time the heating comes on the cylinder will be up to temp.

thks mate for the update ,

on the unvented fitted a lock shield ,but of course understand regs change and been out of the industry 5 years and understand there good practice etc

but ut know they don't always work , lol as a customer may want them on together if they've run out of hot water for a bath and then the heating goes down in temperature

regards to the ch and hw timings it seems as though they want to go back to the hot water priority days, lol

was taught as an apprentice to fit a gate valve or lock shield on the cyl return to aid the balancing of a system and stop the hot water robbing the ch side , bigger the system the more problems i sometimes found

in hot water cylinders you've got a nice 22 mm full bore bypass , so when the ch came on there would be no way to slow the hw down , to push the heat towards the ch side and allow a good balance between the ch and hw and allow complete balance

however on the quick recovery cylinders I understand the point of them was to get the hw heated quick but I would fit a gate valve and close it just a little , would check the differential to ensure I hadnot slowed it too much and thus defeating the object of a quick recovery cylinder

the other reason was it was good for the aid of power flushing and also air locks in systems , so u can isolate the system bit by bit

but know the design of the system is the most important thing , but we all know things get added , a radiator half a mile away and can't get heat to it, lol

just was always taught the practice and stuck with it for around 25 years and always found it a useful aid to have that gatevalve fitted

just hope this doesn't come across as disrespectful in any way , finding my feet on this forum and the last thing I wish to do is offend anyone

 

[chris watkins]

Not rude at all, we all have been taught, then modified what we have found out with experience & hopefully we are all here to learn some more.

Understand where you are coming from on the old balancing but there is a better way I think & it is linked to the old Part L again.

Because the coils are so big in the modern cylinders (aiming to reheat in around 20mins) what we don't want to do is try to do both at the same time i.e. heating & hot water, as most systems / boilers are just not going to be able to provide for both in a reasonable time scale.

Instead why not encourage the use to set the hot water, say to come on first, dedicating all the boiler power available to heat the HW, after around 30 mins program the heating to come on by this time the cylinder will have been heated & the zone valve closed now the boiler will be able to quickly heat the emitters. (once the house is up to temp if the HW needs to top up the drop in heating water will not be noticed)

The main reason we don't want to be fitting the old balancing valve is that a slower flow rate / heat up of the cylinder will lead to boiler cycling which is as we all know is inefficient bearing in mind that for most of the year the heating is not on just HW. I believe this is why the coil sizes of cylinders was increased under Part L.

What do you think ?

 

[oil gasman]

Not rude at all, we all have been taught, then modified what we have found out with experience & hopefully we are all here to learn some more.

Understand where you are coming from on the old balancing but there is a better way I think & it is linked to the old Part L again.

Because the coils are so big in the modern cylinders (aiming to reheat in around 20mins) what we don't want to do is try to do both at the same time i.e. heating & hot water, as most systems / boilers are just not going to be able to provide for both in a reasonable time scale.

Instead why not encourage the use to set the hot water, say to come on first, dedicating all the boiler power available to heat the HW, after around 30 mins program the heating to come on by this time the cylinder will have been heated & the zone valve closed now the boiler will be able to quickly heat the emitters. (once the house is up to temp if the HW needs to top up the drop in heating water will not be noticed)

The main reason we don't want to be fitting the old balancing valve is that a slower flow rate / heat up of the cylinder will lead to boiler cycling which is as we all know is inefficient bearing in mind that for most of the year the heating is not on just HW. I believe this is why the coil sizes of cylinders was increased under Part L.

What do you think ?

thks buddy as i certainally wouldn't wish to offend and agree it's always nice to learn things regardless of how many years in the industry

i see what ur saying with regards to quick recovery cylinders and stopping the boiler from cycling

would u mind if i put this up and how I think it through , yeh I know need to get out more, lol

if for example a gatevalve was fitted onto the return of a quick recovery cylinder

going for for a recovery time of 25 mins

if the ch is on at the same time the boiler shouldn't cycle too much as it would go on and off on the boiler stat and of course what the demand call is

so of course want the heat out the boiler as quick as possible and back for reheat , with a differential of between 15 to 20 degree differential

if then the ch goes off and there is too much restriction via the gatevalve i agree it will slow the reheat of the cylinder and could cause the boiler to cycle if it can't get a decent differential

but if the circ is say a 15/60 instead of a 15/50 the boiler should then be prevented from cycling as the heat is leaving and returning to the boiler quicker, lowering the differential and thus preventing the cycling

so that when the ch comes back on it allows the hw to not rob everything and allow the furthest rad to heat and give a better balanced system

But , then understand there could be a higher possibilty of cycling on the boiler in hw mode only , as the cyl gets older

with regards the ch and a rad not getting hot that is far away , then that should have been sized properly

so in other words , gary , don't fit gatevalves on bloody quick recovery cylinders, lol


but ok on normal ones, lol

plus us we all know what customers can be like , asking why does my rad cool off when the hot water is on

but in the same way a combi works , in shutting off the ch when hw is on

hows that

 

[Gray0689]

Not rude at all, we all have been taught, then modified what we have found out with experience & hopefully we are all here to learn some more.

Understand where you are coming from on the old balancing but there is a better way I think & it is linked to the old Part L again.

Because the coils are so big in the modern cylinders (aiming to reheat in around 20mins) what we don't want to do is try to do both at the same time i.e. heating & hot water, as most systems / boilers are just not going to be able to provide for both in a reasonable time scale.

Instead why not encourage the use to set the hot water, say to come on first, dedicating all the boiler power available to heat the HW, after around 30 mins program the heating to come on by this time the cylinder will have been heated & the zone valve closed now the boiler will be able to quickly heat the emitters. (once the house is up to temp if the HW needs to top up the drop in heating water will not be noticed)

The main reason we don't want to be fitting the old balancing valve is that a slower flow rate / heat up of the cylinder will lead to boiler cycling which is as we all know is inefficient bearing in mind that for most of the year the heating is not on just HW. I believe this is why the coil sizes of cylinders was increased under Part L.

What do you think ?

In an ideal world your right but it's far from ideal I'll always put a throttle valve on coil as most people just either turn on hot water only or heating and hot water

 

[chris watkins]

In sort oily gasman increasing the velocity by using a 15/60 will not help as the water passing through the coil or for that matter rads will not have enough time in there to loose its heat raising the return temp back to the boiler, just what we don't want & what the manual by-pass was doing.
condensing boilers all need the 20deg C diff as the modulating controls will try to keep the boiler diff to this & most will have anti-cycling which will hold the boiler off for sometime 20mins.

The fun really starts if you fit a auto adapt type pump which adjust speed LOL.

 

[oil gasman]

In an ideal world your right but it's far from ideal I'll always put a throttle valve on coil as most people just either turn on hot water only or heating and hot water

cheers , it's only from experiance of when customers complain etc and designing the system in order that there happy and it works to there satisfaction but of course within reason

 

[oil gasman]

In sort oily gasman increasing the velocity by using a 15/60 will not help as the water passing through the coil or for that matter rads will not have enough time in there to loose its heat raising the return temp back to the boiler, just what we don't want & what the manual by-pass was doing.
condensing boilers all need the 20deg C diff as the modulating controls will try to keep the boiler diff to this & most will have anti-cycling which will hold the boiler off for sometime 20mins.

The fun really starts if you fit a auto adapt type pump which adjust speed LOL.

oh yes , variable pumps , like the alpha ones , didn't really fit many of them to be honest

worked a lot on Worcester , baxi, potterton, kestons, they were piles of junk , Honeywell controls , inc wiring etc

never went anywhere near the french or Italian boilers walked away from them , enjoyed ufh

spent a couple of years in New York and was taught by some nice Canadian guys about the snow melt systems as well , always good to learn new stuff

but u always get people who think its there way and know everything which I never could stand , always good to learn new ways of doing something