Sucking AIR

[PCDOCTOR]

Dear all

Recently had boiler serviced by BG due to pilot light failing then pump failure and being replaced, All is up and running for now

He recommended that it needed a Power flush after he looked at the pump and wait for it... £550 should do the job !!!

When he saw the look on my face i think he felt a bit sorry for me and said i could try a chemical flush and see what happens.

I thought it was time to pay some attention to the systems so carried out a drain and flush twice !!! Belt and braces

Air was next biggest problem, i could fill 2 radiators in 30 mins no problem ??

After some good old forum searching i looked at the speed setting on the pump and noticed it was left on setting 3

Turned it down to 2 and things were slightly better but not perfect so turned it down to 1 and seems like no air at present

From the attached diagram you can see it is fair size system with 13 radiators and from the noise coming from the area of the overflow pipe towards the pump i can tell it is drawing air down the system at speed 2 and 3

I Could do with turning the speed setting up to improve the speed of the rads heating up and some of the radiators do not get hot (The far ones)

All the info i can find points to setting number 2 is best but need to carry out a mod i think to achieve this

Any ideas

 

[penpusher]

link cold feed and open vent

 

[Dan Robinson]

Nice signature PP.

 

[PCDOCTOR]

Dude

Could do with a little more info

Link the cold feed ? from to ??

Open Vent, If i'm barking up the right tree it is open vented and was working well when the pump failed, i had one hot header tank

Looking forward to what i can only describe as the fastest forumn i have ever seen

 

[gas4you]

Pipe work is wrong. From your drawing the pump is going to suck air down the open vent. The cold feed needs to be teed into the open vent pipe, or along side where it tees off the flow pipe.

Cold feed and open vent both need to be before the pump, if you get what I mean.

 

[chrishutt]

The cold feed coming from the bottom of the feed tank needs to be rerouted to joint the flow pipe somewhere between the open vent connection and the pump inlet.

 

[PCDOCTOR]

Guys

Sounds good to me

If i'm hearing you loud and clear i have modified the drawing for your approval

Should i change the cold feed pipe from 15mm to 22mm when it is re-plumbed or leave as is

Look forward to your reply

Very grateful

 

[chrishutt]

Yeh, that's it exactly. Make sure the flow pipe between vent and feed connections is clear of gunge (see below) or you might get pumping over!

You'll probably find that all the air that has been sucked in before has caused a lot of corrosion of the radiators. Apart from rusty / black water there may well be accumulations of sediment in radiators and on pipe walls. To some extent draining and refilling will help clear this, but it would be must better to flush the system out, perhaps combined with some chemical treatment.

Many people will recommend "power flushing" (which as you already know is pricey) but you can do "mains flushing" yourself without anything much in the way of special equipment. This is described in the FAQ sticky topic and in the Wiki.

Nice diagram by the way. Here's one of mine! (Click to expand - might help you understand why air was being sucked in.)

 

[gas4you]

If possible re-run the cold feed in 22mm as well.

 

[PCDOCTOR]

Dear all

Re piped as version 2 diagram above and so far (4 hours) so good

BUT

If you look at the diagram above you can see 1 isolation valve between the pump and the storage tank

If i'm correct it should be closed

Look forward to your excellent support

 

[croydoncorgi]

That valve MAY be put there to regulate the flow through the coil of the hot water cylinder (assuming that's the valve you meant).
You don't show any controls or motorised valves on your diagram. Are there any? Or is it a 'gravity' hot water system? If so the diagram is a bit wrong - the pump should not be in the path to the cylinder.

 

[doitall]

No that valve should be cracked open as its a by-pass leg for the pump

 

[PCDOCTOR]

No motorised valves fitted yet !!

It is just a basic Water / Radiator with just a all on or off option and controls on the radiators via there local Thermostatic valves

From the info i have been given you recommend the valve from the pump to the storage tank be fully open

I Was just thinking it should have just a flow in, through and out to the return pipework but you are saying it also does a third function and return feed back to the hot side of the pump

Hope when i open this control valve that everything is correct and you more knowledgeable guys can say that it is know piped correctly

 

[chrishutt]

No motorised valves fitted yet !!

Assuming your hot water storage vessel is mains pressure unvented (what it looks like in your diagram), it really must have a motorised valve in the flow pipe as an additional measure to prevent overheating. the link with the valve is a by-pass from pump to return pipe to ensure that the minimum flow takes place through the boiler (for example when both CH and HW circuits are closed).

 

[Agile]

it really must have a motorised valve in the flow pipe as an additional measure to prevent overheating.

While it must have one it does not mean that it does have one !!!