Ideal Mexico Gravity DHW

j1cta · Feb 12, 2011

Hi All,

My First post and new to plumbing and heating.

I’m looking for some technical advice regarding an Ideal Mexico Slimline RS 3/50.

I have an installation which currently uses a Gravity DHW and Pumped CH with all 4 tapping being used in the boiler. All pipework is 22mm and not 28mm as suggested in the manual.

The Left hand side of the boiler is for CH and the Right hand side for DHW.

For each circuit, the feed is at the top and the return is at the bottom.

The DHW does not rise immediately from the boiler but drops below the floor for about a 1m before rising. Horizontal HDW run to the storage tank is about 6m.

The heating seems to be working fine, but the DHW is non existent. Only warming about 2m of the feed pipework.

The manual doesn't really say too much but I would like to know, if each circuit is independent of the other inside the boiler, as it doesn't seem to be. Also there are 2 header tanks (1 large – Cold water and 1 small - DHW/expansion) but only 1 top-up feed to the DHW circuit and nothing to the CH circuit. The CH circuit does fill, but very very very slowly.

Does this all sound something like or is it a total abomination that needs a re-hash to a fully pumped system???

Any help would be appreciated.

Billy Bob Bob · Feb 12, 2011

sounds a mess get a pro in,you say theres only a feed to the dhw but not ch? sounds like a primatic system but that would have just one large tank

j1cta · Feb 12, 2011

Yep. 2 Tanks but only DHW gets its feed from the small 1.
What do you think to the circuits maybe crossing in the boiler?
Has this ever been done on the old cast iron boilers with multiple circuits?

stevetheplumber · Feb 12, 2011

there are no circuits inside the boiler just one space the water in both circuits is fed from the small tank there will be another 22mm pipe from the tank to the base of cylinder to feed hw
gravity circuits should rise from the boiler but we must assume this system has worked
it sounds like you have drained the system as you say its slow to fill you may have an airlock in the primaries up to the cylinder try cracking the nut where the flow goes into the cylinder
pics of boiler and cylinder cupboard might help diagnose this better

j1cta · Feb 12, 2011

Thanks Steve. Yes that all sounds like you've seen this before.

So your saying the 2 circuits are mixed in a single space inside the boiler.

OK so that explains the two circuits (or 1 big circuit) in the boiler situation.

I tried to bleed the DHW circuit with a little cheat. I added a bleed nipple to the primary feed pipe at the cylinder (which goes higher than the cylinder), just before it enters. It bleeds up fine but still no DHW flow. Just 2m getting hot from the boiler on this circuit.

Just a thought. But should the feed from the small tank be into the feed or return?
It's currently in the return (Side/lower cylinder tapping) as opposed to the feed (Side/Upper cylinder tapping) which marries to all the diagrams that I've seen for this type of system.

I'll do a little drawing of the system, and add it to the forum.

The rads bleed fine downstairs but are nearly impossible to bleed upstairs. Its as if theres not enough pressure in the water in to push the air out.

j1cta · Feb 12, 2011

Just drawn the layout.

The DHW pipework is purposefully shown to leave the boiler and travel below ground before rising to the cylinder.

Again, any help is greatly appreciated.

PlumbBobBob · Feb 12, 2011

are you saying that the vent for your hot water goes over the f&e not the cold water tank?

j1cta · Feb 12, 2011

Steveb, little typo on my part.

I've updated the drawing to vent to the right tank.

Bartdude · Feb 12, 2011

I don't see how that gravity hot water circuit will work. The flow from the boiler needs to rise all the way to the cylinder,the way it's shown on your drawing means the hottest water can't flow around the low point that's been created. Also gravity pipework should be in 28mm,not 22.

If the flow was altered it would work but a better option would be to reconfigure the hot water circuit so the system becomes fully pumped,fit zone valves and a cylinder and room stat,bypass etc and the boiler wired to prevent short cycling. It would be much more efficient this way.

It's obviously been in for a while so it's odd that it's not been a problem before,with gravity pipework like that I'm surprised it's worked at all.

j1cta · Feb 12, 2011

Thats what I thought. The boiler manual seems to predict that it wouldn't work but I wanted to get some expert opinions.

The cylinder does have an immersion fitted and I'm wondering if this is what has been used to heat the water rather than the gravity actually working.

The property is very dilapidated and has been bought from a family inheriting from their parents and thus the new owner is looking to update as cheaply as possible.

I've never come across gravity DHW before and wanted to be sure before I advise on changes to it.

Billy Bob Bob · Feb 12, 2011

gravity domestics are common ,best bet combi,just fit a good one (BAXI) and de scale properly

Reg Man · Feb 12, 2011

I agree with Bartdude. There is no way the gravity circuit will work. Im from the old school of heating before fully pumped heating and your example has been carried out by someone who don't know what their doing. Your drawing by the way is great.

I am not sure about a cheap answer to the problem. Lets look at what you've got: Boiler although very good is about 25+ years old and probably contains asbestos on the combustion seal gaskets. Additionally well past its useful life expectancy. Gravity systems by todays standards are very inefficient and not now permitted on replacements or new systems.

Recomendation: Replace boiler for up to date 90%+ efficient model. Up date pipework and controls to a fully pumped system. (Room thermostat, and cylinder thermostat interlocked with the boiler, Thermostatic rediator valves for all bar one rads). Should also consider a proper power flush and installation of a magnetic filter to protected the new boiler.

tamz · Feb 13, 2011

That has never in it's life worked as it is.
Change it to this

and learn yourself a bit more about systems.

j1cta · Feb 13, 2011

Guys, Great comments.

My original comments where to bring the system (especially the boiler) more up to date, but the customer is quite difficult to advise and doesn't want to spend any money.

Will it work on 22mm, cos the whole thing is 22mm, but it's supposed to be 28mm MIN (as per manual). If I make TAMZ changes and it still doesn't work then I'm goosed that'll be at my cost, not the customer.

Will try again with my original thoughts to upgrade.

Cheers guys.

Bartdude · Feb 13, 2011

I would expect it to work in 22mm if the pipe run is not too long. As said before it should be in 28mm but a lot of systems out there aren't.

If the customer is not interested in spending money then altering the pipework is the cheapest option in the short term. Just make it clear that it's not the best way to proceed and the present system is out of date and inefficient at best.

stevetheplumber · Feb 13, 2011

you can leave the return where it is its just the flow pipe you need to alter to run continously upwards from the boiler tapping ,droped returns were quite common and there was a school of thought that says they make them work better
yes id expect this to work in 22

tamz · Feb 13, 2011

It will work fine with 22mm. Just a wee bit slower.

j1cta · Feb 13, 2011

Great guys.

Thanks for all your help. Will let you know what happens.

Reg Man · Feb 14, 2011

I would walk away. custard will throw it back in your face if all goes wrong. Sit by recommendations for an up to date system. Not worth the hassel.

tamz · Feb 14, 2011

There is something not right about this.
The system as it was drawn would never work. The boiler is 10-15 yrs old so something has changed. It will work fine with a bit alteration but if the op is indeed a plumber/eng called out to a job i would be wary.

yorkieplumber · Feb 14, 2011

I would not mess around update system, reg man spot on with advice, your the expert inform customer of your recommendations and explain the ins and outs, if they dont listen walk away as you could end up in bother, you could try messing with existing system but circs wrong size 22mm not 28mm, you mess and it is still not right you wont get paid. Upgrade and it also more efficent cheaper running costs etc, your the expert explain to customer carefully and 99 out of 100 will take your advice, hope this helps have been self employed for 29 years as plumber/heating/gas engineer so i think i have a little experience regarding customers etc.

j1cta · Feb 14, 2011

Will do Yorkie.

j1cta · Mar 1, 2011

Well Guys, finally finished the updating this system. Have been off an on for the last few weeks.

Converted it to a fully pumped/open vented system. Having inserted a couple of manual bleeds to get the airlocks out, and the rath of a dodgy (new) Tank stat, it seems to work OK.

The boiler seems a little louder than I would have expected and takes longer to warm things up (15Kw Max), but it does seem do what it's supposed to do (eventually).

Thanks for all your help. I think I've managed to thank everyone involved.

Cheers

Ideal Mexico Gravity DHW

j1cta

Billy Bob Bob

j1cta

stevetheplumber

j1cta

j1cta

PlumbBobBob

j1cta

Bartdude

j1cta

Billy Bob Bob

Reg Man

Plumbers Arms member

tamz

j1cta

Bartdude

stevetheplumber

tamz

j1cta

Reg Man

Plumbers Arms member

tamz

yorkieplumber

j1cta

j1cta

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