Pump head

[pf_mills]

Just a little advice please.

Boiler in kitchen, two bedroom house.
System now has full TRVs except room with stat.

In the loft I want to put the pump, 3-way valve and bypass valve. The HW cylinder is directly below in a cupboard on the landing.

So flow will be boiler..air seperator (with vent and cold feed)..pump..T for bypass valve..3-way valve.. am using a 5M head pump (3-speed).

Can somebody please advise how high the F&E tank should be above the pump to avoid problems.

Thanks

 

[chrishutt]

Since the feed and expansion (F&E) pipe and the vent pipe are connecting via an air-separator, that will be the neutral point of the system. Between that point and the upstream side of the pump will be under negative pump pressure and upstream of the pump back around to the neutral point will be under positive pump pressure.

The F&E tank should provide enough static pressure to overcome the negative pressure downstream of the pump to avoid creating sub-atmospheric pressure which could suck air in through a minor leak, even if the "leak" doesn't allow water out! Such leaks are quite likely on the upstream pump isolating valve, particularly the spindle gland nut.

This negative pressure will vary according to the setting of the pump and overall resistance to flow (e.g. when all TRVs are shut). I don't know off-hand what this might be but I would guess around 1 metre so if the F&E tank were at least 1 metre above the pump position you should avoid getting sub-atmospheric pressure upstream of it.

 

[pf_mills]

Thank you for your swift reply Chris. Guess I'll give the pump as much head as I can. thats not very well phrased!

I have bought pegler valves for the pump. Guess a bit of silicon on the glands would't do any harm.

 

[chrishutt]

Pegler valves should be of good quality, but just check that the gland nuts are tight. As for giving your pump some head.....I'm glad it's a DIY job.

 

[JohnD]

When I had dandruff, my ex-wife asked her colleagues if they recommended anything. One of them said "Why don't you give him "Head and Shoulders?"

Puzzled, she asked "How d'you give Shoulders?"

 

[doitall]

When I had dandruff, my ex-wife asked her colleagues if they recommended anything. One of them said "Why don't you give him "Head and Shoulders?"

Puzzled, she asked "How d'you give Shoulders?"

Is that the 99 with the flake or the walnut whip.

 

[ChrisR]

I've had cold ones...

 

[pf_mills]

Interesting comments.

So I cant get enough pump head. I have now installed the pump at the side of HW cylinder. Still am putting the relief v/v and 3-way v/v in the loft.

I propose to put the relief v/v return upstream of where the HW cylinder return Ts in. I understand that it is normally downstream of this point.

I can't see a problem with this..is there please?

 

[Agile]

I cannot understand exactly what your arrangement is.

Generally if the vent and feed are close together then if you have at least one metre head above everything then it will probably work.

If things are not optimum then you could need more than the pump head of 5-6 m above the system in the worst case.

One of the most common DIY problems is unvented high points. Fitting screw cap air vents will help deal with this but may need regular bleeding.

Tony

 

[pf_mills]

Thanks Tony for your quick reply. Sorry that all is not clear

As you are probably aware (from previous posts) I’m putting the whole CH system in, including the boiler and doing the bathroom at the same time (the bathroom works). My friendly CORGI man will commission the system etc and do the bits he has to do. We initially had a chat about roughly how to do it and I’ll phone him when its all in. He goes on holiday on 21st and I am away from 29th for 3-months so need to progress quickish now, that’s why I am up at 6am. Luckily my tenant is understanding as we are getting to two and a half weeks now!

I wanted to put the pump etc in the loft, but couldn’t find info on the required head (Wilo pump had no info in the box) so I asked the question and the views were as previous. It would have been difficult to get the 1M head anyway. I later found in grundfos literature that 1.5M is recommended. So decided to put the pump lower.

The supply from the boiler comes up into the bottom of the HW Tank cupboard which is on the landing and the cupboard isn’t very big. I have then fitted a Pegler Ventair Air Separator and the pump now sits to the side of this and feeds up into the loft. The MU and separator air outlet run up into the loft and I have positioned the F&E Tank as high as I can.

All the radiator supply and return pipes terminate in the loft. The bypass sits (in the loft, almost on the floor)) just before the 3-way valve. For ease I want to put the bypass outlet flow into the boiler return line upstream of where the return connection from the HW cylinder heating coil Ts back into this line (obviously after thereturn from the heating system). Normally I believe that the bypass outlet connects into this line but after where the HW cylinder return Ts in. Technically I don’t see a problem with his arrangement.

Thank you for the info on un-vented high points. I will fit something.

 

[chrishutt]

I don't think it matters much where you connect the return from the by-pass valve. Anywhere on the return pipework is OK, provided the pipe is large enough for the flows. For convenience it is often connected to the DHW cylinder return. The by-pass valve can be placed immediately after the pump outlet, so it doesn't even need to go in the roof space with your arrangement.

The only important point is that all the heating returns are commoned (joined) before the return connection from the DHW cylinder to avoid reverse circulation, which I think you already understand. In theory a by-pass return connecting to the heating return pipes before they are commoned could also set up reverse circulation, but this would only occur for the short period of boiler overrun (if any) after the heating motorised valve had shut and would not be a significant problem.

 

[pf_mills]

Thank you Chris.

I didn't think that there would be any problem.

I had thought of running the pipe around the rear of the cylinder and connecting as you suggest. But with all the other pipes around its not easy. I also wanted to make it easyish to cut the tank out if needed at some future date. I replaced it three or four years ago and it is now easy to cut out.

If I was to do the job again I would hook out the HW cylinder, move the pipes around and get all to fit in the cupboard. The problem is that I am slow and have a tenant in the house.

As a point of interest when looking how to run the gas pipe to the boiler..only run and not connect..I pulled out the electric cooker to see what had been done for the hob gas supply.

I found that the corgi guy, who I paid £60, to connect up the hob 4 years ago, had cut into the back of my built in cooker..the air cooling bit..as he couldnt be bothered to raise the gas connection a couple of inches so that the cooker would slot back fully into position without fouling teh cooker... its all black and brown at the back now! another little job to do.

On the point that Tony mentioned, a high point vent. I would be surprised if its needed as its all pretty horizontal in the loft. However I don't want to touch the system once its been cleaned. I'll put a 15mm vertical line in with a valve. Is there a reliable auto vent available and if I install one, even at a later date, can I run it back to above the F&E Tank.

Also as I will be leaving the UK for good next year and the house will remain rented, I have a little worry about freezing. The boiler, an Alpha CD18R has an anti freeze setting, however I don't trust tenants..maybe they will go away at xmas and switch all off. I will probably use Fernox protector as I have some ..but do they do a combined protector and antifreeze? or what is available. Can I add some antifreze later?

Back to the loft now.....glad I don't have to do this for a living...its a pig of a job...

Lucky its stayed warm as I've just hooked out the night storage heaters!
Thanks..no more questions now I hope!

 

[ChrisR]

Is there a reliable auto vent available and if I install one, even at a later date, can I run it back to above the F&E Tank.

Not really, they can all leak given an excuse. Suggest you use a manual vent of a type which doesn't have a rubber seal like "finger vents", they stick shut. There's an all metal type which is like a rad vent and uses the same key. You shouldn't have to vent it more than a couple of times.

Note that auto air vents will let air IN if the system sucks, unless you close the cap - in which case you might as well go manual.


Yes you can get antifreeze (leak-finder!) for heating systems but for what it costs I'd put a frost stat in if you're worried. You need to insulate the pipes pretty well anyway. Make sure the froststat is heated by the heating or you'll have the heating on full all night in cold winters.

 

[doitall]

If you want a good auto air vent the "Spirovent" is the bees knees

Dont do any off the things Chris said above

About 40quid from bss etc

 

[meldrew's_mate]

...I cant get enough pump head. I have now installed the pump at the side of HW cylinder. Still am putting the relief v/v and 3-way v/v in the loft...

Grundfos recommend 0.5m dynamic head as a minimum, so the static head in most cases will need to be about the 1.5m quoted, though higher static head is generally better. They also recommend the flow direction to be vertically up so that air bubbles will easily pass through.
Glad to see you've lowered the pump anyway, I don't like scrabbling around in lofts to change cheapo pumps when there's a lovely warm airing cupboard below. Be sure to route a few pipes around it though, so I haven't got room to swing a spanner.