Boiler question

[HVS]

I have a conventional gas boiler (non-combi), which I've turned off while our water supply has been fixed.

(Long story -- a leaking mains supply; days to get the water company to fix the street stopcock, which was seized; supply pipe now repaired, but another 2-to-3-day wait to get someone to replace the in-house stopcock as that now appears to have gunged up...)

Anyway -- the upshot is that I don't have a water supply to the cold- water tank in the loft at the moment.

So: is it safe to turn the boiler on for a bit of heat, or is that an absolute no-no?

Views appreciated.

[Andy Hall]

Do you have a small tank in the loft for the CH? If so, check that there is at least 75mm of water in the bottom.

If not, the system is sealed and there should be a pressure gauge on the boiler or expansion vessel. Check that that has a pressure of at least 1 bar.

As long as you meet the appropriate one of those criteria, you can safely turn on the boiler.

[Owain]

Should be fine; the boiler should have no direct connection to the mains. If a vented system check there is adequate water level in the header tank (the small one, not the tapwater one).

If it's a sealed system then there shouldn't be a direct connection to the mains anyway; although many people do leave the filling loop connected, it should be stopcocked off at both ends.

It may be a good idea to tie up or stopcock off the ball valves to the loft tanks and run lots of water through the kitchen or other direct mains tap, as the water may be gritty when the supply is reinstated.

Owain

[Roger Mills]

The short answer is yes, it's perfectly safe.

The slightly longer answer . .

I'm assuming that it's a vented system, so you will have two header tanks in the attic. The large one is the cold header for the HW system. Once that is empty, you won't be able to get any hot water to the taps even though the HW cylinder is full of hot water, 'cos it needs cold coming in at the bottom to push the hot out of the top and onwards to the taps.

The small tank is the fill and expansion tank for the primary heating circuit. This is the water which circulates from the boiler through the radiators and through the heat exchanger coil in the indirect cylinder (so as not to mix with the hot water which comes out of the taps). The primary circuit is essentially self-contained, and doesn't need a constant cold supply once it is full - with the ball valve only needing to open very occasionally to replenish any water which may have evaporated (which is why many ball valves in F&E tanks seize up with dis-use - but that's another story). So check to make sure that there's a few inches of water in the bottom of the F&E tank - just enough to cover the outlet pipe in the bottom when the system is cold - and you may then safely run the boiler.

If there's still some cold water in the large header, you will also be able to get some hot water out of the taps, but use it very sparingly because the cold won't be replenished and once it's gone it's gone!

HTH!

[HVS]

On 02 Oct 2007, Roger Mills wrote

Many thanks -- it is a two-tank system, and there's water in both tanks; there's a dribble of water going into the CW tank -- it takes a long time to fill up, but it seems to have filled overnight.

(Heat! Yay! Missus will be pleased!)

[HVS]

On 02 Oct 2007, Andy Hall wrote

Yes, there's a small CH tank in the loft, with water -- so I've now turned on the heat.

Many thanks; it was getting a tad chilly overnight in here.

[HVS]

On 02 Oct 2007, Owain wrote

It's a vented system, and there's water in both loft tanks.

-snip->

I'll make sure I do that; many thanks for the advice.