Replacing loft tank

[dave887]

Our 100 Gal galvanised loft tank is developing a slow leak and needs replacing.
The plastic ones seem ok BUT our dhw is heated by a Rayburn regent which occasionaly will boil over, and I realise that we can't have the expansion pipe pouring boiling water into a plastic tank, but no one seems to sell galvanised anymore.

I was thinking of adding a towel rail/radiator to the boiler output to act as a heat sink. Could I then direct the hot water expansion pipe outside as an overflow?

Any suggestions welcome. we don't really want to get rid of the Rayburn.

 

[david williams]

you can still get galv tanks to order,you can get heavy duty plastic tanks,plastic tanks need proper suport across base,22mm marine ply minimum.if worried about expansion take it outside to a safe discharge point so as not to spray passers by with hot water

 

[justlead1]

Hi. I can understand your dilemma. There have been a couple of dreadful incidents where plastic cisterns have failed, due to systems boiling and heated water replacing the cold in the cistern, resulting in collapse .
However when viewed against the number of occasions where this happens accross our country, leads me to belive other important factors were ignored. New type cisterns need to be supported completely across the base (not with chip board) and the connections of pipes spaced apart, so as not to weaken at any one point. making them fit for purpose. As to the venting suggestion, it would waste water, which would not comply with the water regulations and in the event of freezing create a far more dangerous situation than that in the post. Good Luck

 

[dave1]

I had a job yesterday where the expansion was running boiling water into the cwsc, faulty immersion. it was a plastic (rectangle) tank and held its shape when i turned up the customer reported seeing the tank moving due to the, i removed the tank lid and could not believe the steam that came off, although the tank held it shape it was quiet soft/ flexible when i arrived, i would imagine that these tanks are tested to high temperatures. I have heard of storys where the older round collapsable plastic tanks have folded due to the heat but do not know whether this was due to bad installation or not.

 

[Plouasne]

I used to use the Sarena fibre glass CWST's, these were rectangular with a stiffening band around the middle of the larger sizes, far superior than the plastic round ones

 

[dave887]

Many thanks for the comments. I should be ok with a Polytank as it meets BS4213 (capable of withstanding boiling water) and will be supported on 22mm WBP ply.

I was going to ask about adding the rad but I guess I should put it as a new topic in heating.

 

[david williams]

plastic tanks need to be supported properly.as for waste of water if hot vents into tank ,tank overflows through overflow anyway,vented through roof when not venting water level in vent pipe not outside roof level,when venting would have to be dam cold to freeze hot water.

 

[justlead1]

When a system over heats is does not necessarily over flow as the water from the vent is replace via the cold feed forming a circuit. I have witnessed water vapour freezing on an outside vent pipe to a hot water system. Certainly i would note under right the risk. Good Luck

 

[david williams]

if there was hot water in the vent pipe when this accured how low was outside temp

 

[justlead1]

Hi. David the vapour seamed to condense on the 180 degree bend and the drip from the vent froze forming an icicle which blocked the vent. Under condition of strong wind and approx. 2 degrees below freezing. (At the time i was running a 24 hour service, (the result a collapsed cylinder when the client tried to reduce heat in cylinder by tuning on taps) ended by digging the hot coals from the solid fuel appliance.

 

[Torsionbar]

My parent's Smokeater back boiler regularly boiled over into the plastic indirect CW tank (the is was Osma in what looked to be identical plastic to the main tank It carried on doing this for years with any effect till bloier was replaced with gas and it is is still OK after 29 year

Glass fibre tanks where often fitted in the 1960/70's in place of galvanised - not sure whether these can be had but I used one as a rubble carrier until it got flattened - they are very durable

 

[Plouasne]

Any body else remember the Osma plastic hot water cylinders, and how they used to come unglued around the joining seam, which was half way up the cylinder