no hot water

robmar0se

The problem is that we are not getting hot water. Let me explain the system as it is pretty antique.

We have a oil boiler which is firing fine, with 3 circuits (2 radiator circuits and one water) each circuit has its own thermostat which each works a mechancial switch. The bathroom radiator is on the same circuit as the hot water. Hot water is stored in a lagged copper cylinder. At the moment the central heating thermos are set to effectively off.

The problem is that the timer swtiches the boiler on, the bathroom radiator get quite hot, but the boiler cuts out before the water in the cylinder is heated up as it used to.

Thinking aloud, it can't be the mechanical switch as the radiator in the bathroom heats up. No sign of any leak. Plus the builer will heat the other circuits when tried.

So would you concur that maybe we should change the thermostat on the cylinder? Any other suggestions to eliminate other possibilities?

Thank you

PS Is there a way of testing thermo's?

keystone

Your bathroom rad/towel rail will more than likely be on the primary circuit before the motorised valve. It acts as a bypass as well as poviding a modicum of heat in the bathroom. Its bound to get hot but as there is no circulation it gets hot as that part of the circuit gets hot until the boiler stat kicks in and shuts the boiler down.

With the system set to DHW only the cylinder stat will call for heat if the cylinder is cold. If the cylinder stat calls for heat the boiler will fire so no I don't suspect the cylinder stat I suspect the DHW motorised valve (what you are calling the mechanical switch). Either its full of carp and stuck - remove the head and try to operate it mechanically using a pair of pliers or grips or the head itself has failed.

Cheers

robmar0se

keystone wrote: »

I suspect the DHW motorised valve (what you are calling the mechanical switch). Either its full of carp and stuck - remove the head and try to operate it mechanically using a pair of pliers or grips or the head itself has failed.

Thank you.

I thought about that too, but thought that it might not be that for two reasons.. (i) all the motor valves/pump are near the boiler, whereas the bathroom rad is on the other side of the house (and I don't think it warms up when the other rads are on - I'll test this again (ii) there are a couple of pipes near the cylinder which are also warm to the touch, one hotter than the other, but not too hot to touch. The other reason why I haven't looked at the motor valves is I would need to pull carpet/floorboards up, but may have to do this, darn it.

keystone

If the bathroom rad is on the primary circuit it won't warm up with the CH. It will warm up with the DHW which lets you have toasty towels when you don't need the heating on and also (as earlier) acts as a bypass. I hear what you say about valves in one place and bathroom rad in another but I can't see it myself so am sort of feeling in the dark a bit.

Cheers

robmar0se

robmar0se wrote: »

I don't think it warms up when the other rads are on - I'll test this again

Just tested this, the rads on the central heating circuits are v hot whereas the bathroom rad is just warm. So would this discount the motor valve as the problem?

PS I believe our posts overlapped. I guess that I don't understand "primary circuit". You say that the above test doesn't prove that it isn't the motor valve - job this w/e is to move the furniture, pull back the carpet and have ago with the valve - (have done this a few years ago before we redecorated).

keystone

On a conventional fully pumped vented system with an indirect water system, the copper hot water cylinder contains a coil of pipe. This coil forms part of a run of pipework attached to the boiler. It is heated directly by the boiler. Indirectly, it heats the water in the cylinder. Flow to the radiators off this circuit will be controlled by one or more motorised valves which will operate when the house says its cold. The "primary" circuit is the flow and return pipes to and from the boiler via the cylinder. The bathroom radiator/towel rail is normally installed on this independently of the CH radiators. Not sure I've explained it that well - if not let me know.

Cheers

robmar0se

keystone wrote: »

The "primary" circuit is the flow and return pipes to and from the boiler via the cylinder. The bathroom radiator/towel rail is normally installed on this independently of the CH radiators. Not sure I've explained it that well - if not let me know.
Cheers

Thank you once again Keystone.....

It is either the motorised valve or the thermo? And in the situation where the ch rads are hotter than the bathroom rad, and the DHW is not working (depending how the pipes run) would it not be inclined to think it was the thermo, or is there something here, (in the words of Ed Milliband) I'm just not getting?

keystone

A picture is always worth a thousand words:




2 zone valves for heating as you say you have.

Yellow pipe work is primary circuit

Towel rad normally installed across primary flow and return thus independent of CH.

If cylinder stat is calling for heat and boiler fires up then sounds like cylinder stat is OK. If you operate the temp control on cylinder stat does it click on and off? Its only a switch. Check the hot water water valve as suggested .

Cheers

robmar0se

Keystone, Much appreciated I now understand, if I could I would give double thanks. Will report back after tomoz............

robmar0se

Back again!

Well tested all motor vales - all okay. However the DHW valve is permanently open. Boiler heats water and then shuts down leaving us without hot water in the cylinder, pipe before after valve is hot, also one 25mm pipe near cylinder is hot.

Does this infer a pipe blockage somewhere? Should I drain down the system, flush and try again? Do you think this might solve problem, or does the 38yr old cylinder need replacing? We are in relatively soft water area, and get some furring but not bad at all.

keystone

If DHW valve functions OK but permanently open means stat always calling for heat (well it would be if the cylinder is cold) when the timer allows it to.

So its becomes a circulation problem and yes it does possibly infer a blockage. Is the circulator functioning OK? If so lets go looking for a magnetite blockage - particularly given the antique nature of your system. The usual suspect is where the feed (from the F&E tank) joins the main pipework. If it is magnetite it will be absolutely solid and no amount of draining and flushing will shift it. The affected pipework has to be cut out and replaced. If there is an air separator on the vent pipe that might also be blocked.

Sorry this is taking some time but remotely its a case of eliminating possibilities one by one.

Can you post a pic of the cylinder and the pipework around it and put some narrative with it to say which pipe is connected to what - flow and return to boiler, vent to roof, cold feed, which is the hot pipe near the cylinder etc. That might help a bit.

Cheers