My cylinder (storage water tank) thermostat is an odd one - the dial has numbers 1-9. Currently this is set 5. I'm having to switch this on to heat the water as the boiler is not storing hot water in this tank/supplying it to the taps.
The boiler thermostat is set at 2 (1 being for summer and 4 for Winter months)
I am presuming you are referring to switching on the electric immersion element to heat the water.
From the information you have given it sounds like the mid-position valve (3 port valve/diverter etc) is jammed to central heating. Have a look at it and see.... try manually moving it to the mid position as a temporary fix so it heats both.
Either this or for some reason your cylinder coil is airlocked which is unlikely unless you have had some work done?
Does the hot water heat up when the central heating is on? (you'll have it on soon anyway no doubt)
I once lived in house where in the summer I would have to have the programmer set to both (ie heating and hot water) to come on but have the room thermostat down (like at 17 degrees) so the rads don't heat as the ambient house temp was above 17 degrees and thus the CH wasnt calling for heat whereas the hot water stat on the cylinder set at 60 degrees was..... bingo hot water.
Its a work around.
If your only reason to get £1900 worth of boiler is the problem you are having, I wouldnt bother, and focus more on sorting this problem out.
Im only a DIYer and I'm sure the likes of HTG Engineer et al will be able to advise better, but it sounds more and more like an airlock...... try touching the feed and return pipes that come out of your hot water cylinder.... when they should be hot with the boiler running. They should both be hot to the touch.... if the bottom one isnt, your coil is airlocked inside the cylinder.
The holes on the side are the feed (top) and return (bottom) with the hot water draw off at the top and immersion space just below. You should have pipes to touch in these locations. Remember the rotation orientation of the cylinder might be different in your house but the principle is the same.
If, indeed the coil is airlocked, you just need to crack open a nut and reclose it when the air has escaped and water starts to come out. 5 minute job that might save you £1900!!
If it isnt this, its beyond the scope of my knowledge I'm afraid!
Another thing to check is that you dont have any overflows dripping from the loft tanks to the outside as it may be an entirely different problem altogether.
If on the programmer you cannot have central heating on, by itself then it's a gravity hot water system you shouldn't have a three port valve on your system.
It's either an airlock or a blockage in the primary circuit, Get an engineer out to check they will probably pull the stat and boil the airlock from the system, it's the quickest and most effective way.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!