Is this a problem ... ?

Inigo_Montoya

Sorry ! please move this thread to the DIY / plumbing section ....

Hi

My boiler is situation on the ground floor of my dinning room

The "return" pipe has been routed UNDER the ground floor floorboards for quite a few feet prior to reaching the boiler return inlet just above groundfloor level

As that part of the return pipe is the lowest point in the system then just how likely is is that this could end up being a blockage point some time in the future ?

I assume if it got completely blocked then the pump would break ?

regards

p.s. the feed pipe also used to be routed like this but I re-routed it because of the same concern and because I thought it was more dangerous to get a blockage in the feed pipe i.e. so there was no way to relieve pressure via the overflow pipe into the header tank

Biffa

I have no idea about the down pipe, but at our last house we went through 4 pumps on the boiler, due to sludge in the radiators slowing it all down. British Gas (bless their cotton socks) wanted £700 + VAT to wash it all out. We did it ourselves! We took all the rads off one at a time, took them into the garden and flushed them through with a housepipe, put them all back on and it worked fine.

So basically, yes if there was a blockage the pump would break, but like I say, I don't know about the down pipe. I'm sure someone else will know though!

Inigo_Montoya

thanks for the reply - I have taken the route of using a chemical cleaner and draining down the system to remove some of the sludge - I had to replace the pump just recently as it was very old and noisy (due to a worn bearing I was told) and I used a chemical cleaner prior to replacing it

I ended up opening a small can of worms as I subsequently found the heat exchanger coil inside my hot water tank had sprung a leak (possibly due to the cleanning) and so I had to buy and install a new tank as well ! - screwfix.com do cheap tanks BTW

Also having replaced my pump I now find that water constantly flows into the header tank from the overflow pipe - I assume this is because the pressure produced by the new pump is greater ? - at some point I will try raising the height of the overflow pipe and/or header tank to see if this helps - in the meantime I have extended the overflow pipe so its end is now IN the header tank water which removes the dripping noise and hopefully reduces the extra amount of air getting into the water (which causes rusting I have been told)

Biffa

Maybe you could PM moneysavingplumber and see if he can advise? I'm afraid all I know is from previous experience, I'm better at fixing cars than central heating!

alanobrien

There are a few main reasons why a pump would break
these are;

Worn bearings - due to abrasive particles in the system
Corrosion - due to lack of inhibitor in the system
Motor burn out - due to sludge and/or other contaminants effecting the bearing torque
Cavitation - due to air drawn in at the pump impellar.

All are avoidable providing the system is comissioned and
maintained correctly.

moneysavingplumber

Inigo_Montoya wrote:

Sorry ! please move this thread to the DIY / plumbing section ....

Hi

My boiler is situation on the ground floor of my dinning room

The "return" pipe has been routed UNDER the ground floor floorboards for quite a few feet prior to reaching the boiler return inlet just above groundfloor level

As that part of the return pipe is the lowest point in the system then just how likely is is that this could end up being a blockage point some time in the future ?

I assume if it got completely blocked then the pump would break ?

regards

p.s. the feed pipe also used to be routed like this but I re-routed it because of the same concern and because I thought it was more dangerous to get a blockage in the feed pipe i.e. so there was no way to relieve pressure via the overflow pipe into the header tank

Personally I think you need a decent professional in to advise you. Pumping over is usually down to a blocked cold feed/vent, and chemical cleansing won't usually shift it alone. I'm concerned that you should have the position/route of the boiler flow in regards to the vent checked by a professional as well. I'm not one to generally be alarmist but if it is incorrectly piped (especially on an old floorstander which it sounds like) then in the event the boiler stat fails it can be very dangerous, especially in the likely abscence of a specific overheat stat.

An additional reason for a pump failing prematurely can be when it has been incorrectly oriented, i.e. with the face of the impeller looking towards the floor, they should tip slightly upwards if installed on horizontal pipe work.

Central heating returns often return to the boiler under floor level and should not directly contribute to sludging provided the rest of the system has been installed and maintained correctly. The main cause of sludge in gravity-filled systems is incorrectly positioned cold-feed and vent in relation to the boiler and pump, and the main cause of limescale even in boilers treated with inhibitor is undersized flow and return pipe work and (on gravity hot water/pumped heating systems especially) insufficient 'heat-leak' circuits and abscence of boiler-interlock via cylinder stat and zone valve for summer use when the heating is off.

Inigo_Montoya

alanobrien wrote:

There are a few main reasons why a pump would break
these are;

Worn bearings - due to abrasive particles in the system
Corrosion - due to lack of inhibitor in the system
Motor burn out - due to sludge and/or other contaminants effecting the bearing torque
Cavitation - due to air drawn in at the pump impellar.

All are avoidable providing the system is comissioned and
maintained correctly.

the bearing(s) was definately worn as the old pump was very noisy before I replaced it

the old pump was fairly old - it was already there when I moved in about 10 years ago - I suspect the worn bearing(s) were down to its age and a combination of the factors you mention

What worries me now is that for a handful of seconds when the new replacement pump starts up there is some cavitation before it settles down which is likely to cause premature breakdown - from info in moneysavingplumbers reply I suspect one reason for this may be due to a partial blockage in the cold feed from the header tank

Inigo_Montoya

> Pumping over is usually down to a blocked cold feed/vent, and chemical cleansing won't usually shift it alone.

Could well be an issue although it only started pumping over AFTER the chemical cleaning and only with the new pump

> I'm concerned that you should have the position/route of the boiler flow in regards to the vent checked by a professional as well. I'm not one to generally be alarmist but if it is incorrectly piped (especially on an old floorstander which it sounds like) then in the event the boiler stat fails it can be very dangerous, especially in the likely abscence of a specific overheat stat.

OK sure I can get that checked - I rerouted the feed pipe so that it goes straight up towards the header tank rather than firstly under the floorboards - the order of things is vent, cold feed then pump which I believe to be the correct order ? - the re-routing was done over 5 years ago

> An additional reason for a pump failing prematurely can be when it has been incorrectly oriented, i.e. with the face of the impeller looking towards the floor, they should tip slightly upwards if installed on horizontal pipe work.

The pump is installed vertically - I was told its best to get it as exactly vertical as possible to reduce wear

> Central heating returns often return to the boiler under floor level and should not directly contribute to sludging provided the rest of the system has been installed and maintained correctly.

I was concerned that being the lowest point in the system then that is where all the sludge would collect but you seem to be saying that this set up is not uncommon and just to make sure the system is configured & maintained correctly ?

> The main cause of sludge in gravity-filled systems is incorrectly positioned cold-feed and vent in relation to the boiler and pump

I believe I have them in the right order - I dont know if there are any other considerations ?

> the main cause of limescale even in boilers treated with inhibitor is undersized flow and return pipe work

22mm & inhibitor treated by myself - should be ok

> and (on gravity hot water/pumped heating systems especially) insufficient 'heat-leak' circuits and abscence of boiler-interlock via cylinder stat and zone valve for summer use when the heating is off

lol, bit to much jargon for me ! - not sure what a "heat-leak circuit" is ...

I do have a cylinder thermostat but if not configured correctly it can annoyingly switch the pump off even when the radiators havent warmed the house up properly i.e. the water in the cylinder has reached its max temp BEFORE the house is warm enough - to quickly resolve this I reduced the max temp. on the boiler thermostat and slightly increased the max temp on the cylinder thermostat from 60 to 65 degrees - I have read its about 70 degrees when limescale starts forming ?

I guess the cylinder thermostat should only really close off the water supply to the cylinder and not close down the pump ?

When you use the term "zone valve" are you talking about that three way valve that controls if the water goes to the cylinder, radiators or both ?

In my system you cannot have the radiators on without the hot water circuit being on as well but you can have the hot water circuit on without the radiators which is obviously for summertime - is this common ? - do some systems allow the radiators to be on without the hot water circuit being on ?

moneysavingplumber

Sounds a little odd, if you have a fully pumped configuration with a mid-position valve you should be able to run the heating and hot water independently of eachother. You may have been left with the old programmer that won't let the heating slider go accross without the hot water, or you may have a fault in the set-up or wiring. Limescale in the boiler is not the same issue as limescale in the cylinder. 22mm primaries are fine if the boiler is rated under 60,000 btu but they should be 28mm for that and above usually, even when the boiler tappings provided are 22mm.

The cold feed and vent entries should be no more than 6" apart at the highest point on the flow within the living space usually (although usually at least a metre below the bottom of the f & e tank, and modern schematics usually show the cold feed entering the pipe work from underneath, i.e. curling back on itself. Some boilers recommend air separators and minimum dimensions for the vent to extend at a 45 degree angle above the f & e tank before bending over to vent, for example. Any of these factors being incorrect can aid air ingress and the formation of sludge.

There's a chance that the blockage is the result of residue in the base of the f & e tank being washed into the cold-feed whilst refilling after flushing, or it may have simply been dislodged from elsewhere and found a home there.

moneysavingplumber

Inigo_Montoya wrote:

> Could well be an issue although it only started pumping over AFTER the chemical cleaning and only with the new pump

Is the pump oversized? A Grundfos 15-50 is suitable for most small houses, 15-60 is big enough most town houses and work very well on much larger applications too. Unless you have a very small circuit, then even a 15-60 would be unlikely to pump over if it's sited on the flow after the cold-feed and vent, I've never seen one do it without a blockage even when run on the top speed setting.

moneysavingplumber

Inigo_Montoya wrote:

I guess the cylinder thermostat should only really close off the water supply to the cylinder and not close down the pump ?

That's right, it should just switch the valve accross.