UKC

Following CaptainParanoias central heating issue I thought Id see if I can get any further with my plumbing issue.

Have a fairly old system Glow worm 45-60 boiler in an indirect vented system (i.e heat exchange pipes in hot water cylinder).  The central heating works ok (fairly new pump) but the there is no hot water. (We can get hot water via immersion heater only).

The hot water is meant to flow up into the cyclinder pipes due to hot water rising and the cold water descending to the boiler (no pump). As far as I can see there is no diverter valve - or will there be one hidden somewhere (bathroom floorboards? - if so this could be the problem). My first question is - Is there bound to be a diverter valve in such a system?.

If there isnt a diverter valve what would stop the hot water getting hot if you just have the central heating on (when hot water is working) ?  

If there is no diverter valve then presumably some blockage - but the cylinder is directly above the boiler with only a about 6 feet of wide (28mm I think) diameter pipe between the 2. I assume the boiler just heats the same water that just goes to the cylinder or central heating or both depending on controller settings. (Controller is a Drayton LP520 - fairly new).

Any advice?

Cheers
Steve

I'm a bit confused. Your initial description sounds like a gravity fed system, (no pump so both hot water and rads run off header tanks and convection.

You then say the central heating is pumped, if that's the case the feed to your hot water tank heating coil would surely be pumped too? 

Edit: Nope, I'm wrong, you can get mixed systems. Everyday's a schoolday. 

There would have to be a valve to start flow through the water cylinder though, otherwise you'd have permanent hot water.

Hello Ridge. The central heating is definitly pumped but the hot water isnt pumped up to the cylinder - it just uses the flow caused by heating the water. It is all the same water though - fed from a header tank in the loft. A seperate header tank feeds the secondary water into the cylinder that goes to the hot taps.

Thanks Steve, I had a check and those systems do indeed exist. Never had one so can't really help, other than there has to be a valve to stop/start water flow through the hot water cylinder.

Have you tried setting it on hot water only with room heating switched off?

The new pump may be set for too powerful a flow. This means that the convection flow for hot water is overwhelmed by the pump "stealing" all the flow for  the radiators.

Hi Rick, yes have tried hot water only - but no success

Steve

The old system (which was also a Glow Worm) in my parents' house didn't have a valve stopping circulation that I'm aware of.  If you chose heating, you got hot water too.  If you chose hot water, the heating pump didn't run but some of the radiators got slightly warm through convection.

We did get warm upstairs radiators with just the hot water on, but pretty sure we didnt get hot water with the just the central heating on 

Hi Steve.

Have you looked for any air vent fittings at the high point of the coil  piping near the hot water cylinder?

You could try following the wiring for another clue as to whether you have a failed motorised valve lurking under the floorboards.

I'd assume from what you describe (particularly not working when the heating is off) that the thermo siphon loop isn't working, it could be blocked (valve, sludge, kink, something weird like a dead mouse) or there could be an airlock at the top of the loop or, assuming it's vented at the top, it may just not be filled high enough.

Presumably the heating and heat exchange loop system is topped up from a header tank, I'd check it's full and that nothing has fallen in or died in it and blocked the outlet. Leakage or evaporation (if there's a separate vent) may have then dropped the system water level below the hot water tank even if the header is full.

Check to see if there's a bleed valve near the top of the system, I know some of the loops in my parent's old place had automatic air bleeds where a vent was impractical. I'm not really sure how well they ever worked, something in that rat's nest of a system was always stuck or leaking.

If you run the hot water for a bit you may be able to feel how high up the heat exchanger feed pipes the convection/fluid gets.

jk

As Rick has said you should be able to “bleed” the air from the coil in the Cylinder. There will be a vent point somewhere (hopefully)

If you are getting hot water through immersion then it means there’s no flow through the coil in the HWS cylinder.

Try venting all your radiators to make sure there is no air in the system. Failing that you may need a flush or the coil may just be furred up through age or the inside of the cylinder caked in calcium and just not transferring the heat. Are you in a hard water area?
 

In that case there's almost certainly some sort of valve.  My parents' system is a choice between hot water (with slightly warm upstairs radiators) or both.  There isn't a "just heating" option, as there's no valve.

You have gravity hot water and pumped heating system. There should not be any zone valves on the 28mm gravity pipe work. You might have a blockage where the cold feed from the F+E tank joins the gravity return pipe. Also the heating pump could be set to high. When was the pump replaced, is it fitted the same way round? If its pumping in the wrong direction that can stop the gravity hot water working.

Check the header tank, could be ball valve seized and tank dry.

I

Hi - the ball valve and header tank are ok though there is some gunge in the bottom

A blockage in the feeder pipe is a possibility but there is a heated towel rail in the bathroom that is higher than the feed into the cylinder and that gets hot when central heating on.

I dont think we are in a hard water area but it is quiet old so could well be furred or gunged up - but pipes are wider than central heating pipes - maybe the extra pumping is enough to keep the flow though that though.

 > As Rick has said you should be able to “bleed” the air from the coil in the Cylinder. There will be a vent point somewhere (hopefully)

There is an open vent pipe from the cylinder inlet up into the loft - overhangs the header tank

There is a vent pipe from highest point of the flow pipe where it enters the cylinder. There is a heated towel rail (part of CH) that is higher than this and that gets hot with CH on - 

Thats possible but Id have thought that would affect the CH too upstairs at least 

The flow pipe (outlet from boiler) only gets hot very close to boiler. Even a foot away its isnt hot. 

The limescale will be on the inside of the tank. Are the inlet and outlet pipes hot, but just no hot water? Is the water warm at all or cold, has it suddenly started or been getting worse? 

youtube.com/watch?v=SV2vdGPLRiY&

That’s puzzling. You must have a valve somewhere as it sounds like there’s no water flowing from the boiler when you have it set to hot water only. Follow the inlet pipe to the hot water cylinder. And have a look round the pump area. 

Can't help re: the hot water issue, and hope this doesn't sound alarmist, but there was a very nasty accudent in 2008 caused by a combination of a faulty thermostat on an immersion heater causing hot water to be dumped into the header tank and the header tank not being fully supported underneath.

Might just be worth checking your header tank is well supported while you're up there.

That's an expansion pipe for the water in the cylinder to expand and the excess go somewhere.

The heating coil water is separate from the main tank so that pipe isn't connected to the water in the boiler.

I'm not sure how much head those centrifugal CH pumps can generate but if the system weren't filled all the way up to the top the thermosiphon hot water system would fail but you may still see the CH pump lift water a few feet higher into the top radiators, if you bled them with the pump running they'd probably stay full even when the pump shut down (no way for air to get into them).

I'd still be double-checking for a motorised valve but do check the header tank is actually filling the system.

The heating T's off the hot bit presumably?

jk

The vent pipe comes off the flow pipe just before it enters the cylinder (highest point of primary heating circuit apart from header tank) so (in theory) there shouldnt be an air lock

Hi yes good points - 

Re the T junction - I assume so - cant see it as its at the back of the boiler.

If there is sufficient fluid in the primary circuit (H/W flow & return from boiler to cylinder), there isn't much that could be wrong on a gravity system like this. Air locks have been discussed, if there are no valves fitted (sometimes a check valve was fitted on the return) the next likely issue is a blockage. A quick indicator would be to use a magnet applied to the copper pipes. If there is an attraction, it will indicate a build up of ferrous deposits ("sludge"), likely spot is where cold feed/expansion pipe from header tank joins primary circuit. 

If there is a blockage, cut out and replace pipework section.

If it was my property, I'd be looking to upgrade the system - this is about as expensive to run as systems get. I appreciate you may not want to or be in a position to do this, just thought I'd let you know in case you weren't aware.

Hope you get it sorted.

I

How old is the boiler and cylinder?

you most likely have gravity circulation from the boiler to the cylinder .

it is either airlock or dry or blocked .

How many header tank(s) in the loft or above the cylinder height please?

Yep there is some magnetic attraction around the flow pipe where you mention and return pipe from the cylinder.

Pretty old - probably from when house built in 60's.  It is, as you say, gravity fed circulation.

2 header tanks in loft - one large one for hot water cylinder, and one small for the primary circuit (CH and boiler)

Steve

Have you tried running the boiler on water only and seeing which pipes get hot and how far along they heat up.

set the boiler thermostat on high .

By "Flow Pipe" you mean the water to the taps, flow pipe?

I think its the 'official' name for the pipe from boiler to the cylinder (coil) 

Normally flow is from heat source to load. 
 

So boiler to coil/radiators is flow, coil/radiators back to boiler is return. 
Cylinder to taps is flow. 

So flow will depend on what part of the circuit you’re using. The diverter valve will usually be in the flow and divert  between coil or radiator. The pump will be between the boiler and the valve.