Hot Water problem

[Grant]

Hi,

Every few days when I get up to have my morning shower I find that the hot water is not as hot as it should be so I need to adjust the shower mixer. The water is heated by a gas boiler which is also used for the central heating. The central heating appears to be fine and the hot water is usually OK - I have this problem maybe one day every three or four. I know it's not just the shower because the water from the taps is also affected. Could it just be a dodgy thermostat on the hot water tank, or perhaps something more sinister (and expensive)?

Cheers, Grant

[Set Square]

You need to tell us a bit more about your system before we can give a sensible answer.

Are both HW and CH circuits pumped, or does HW rely on gravity (convection) circulation?

If fully pumped, how many motorised valves are there? [There will likely be either one 3-port valve (Y-Plan) or two 2-port valves (S-Plan) - see

for details.]

If the HW uses gravity circulation, is there any sort of valve controlling the flow? [You may have a 2-port motorised valve in the unlikely event that you have a C-Plan system, or you may have a thermostatic valve such as a Drayton Cyltrol (rather like a big thermosatic radiator valve)]

Is your system vented or sealed/pressurised? If vented, is there adequate water in the small fill & expansion tank (not the large header tank) in the attic? If pressurised, what are the pressures when the system is a) cold and b) hot?

[Grant]

I think they are both pumped. That is, I can hear a pump going when either the HW or CH are on.

I have no idea, which probably means I'll have to get an engineer to have a look at this for me.

It's a vented system. I have no idea about the small fill & expansion tank. Is there an easy way to check that the water level is adequate?

Thanks for your reply, but it appears that I don't have enough information for you!

Cheers, Grant

[Set Square]

You should be be able to find your motorised valves if you have any - most likely in the airing cupboard, or possibly near the boiler. A 3-port valve looks like

(but not necessarily that way up). A

2-port valve is similar, but only has 2 water connections rather than being T-shaped.

I would put my money on it being a 3-port valve - which has partially seized due to sitting in the HW position all summer - and which is now sticking in the CH position. But have a look and see what you can find.

The outlet pipe which feeds the system is at or very near to the bottom of the tank. This must be covered at all times - otherwise air will be drawn into the system and the water won't circulate properly. The level is maintained by a ball-valve. These sometimes stick closed because they don't have to open very often. Then, when the level drops due to a leak - or even evaporation - the ball valve fails to operate, and you have a problem. If the ball is above the water, and not floating in it, that would indicate that it was stuck. If you just tap the ball very gently, you should hear a hiss. Having said all of that, you don't want *too* much water in the tank - otherwise it overflows when the system gets hot - causing another set of problems!

[TheScullster]

If you have a timer controlling hot water heating, it could be this needs changing, maybe to allow for British Summer Time hour change. If someone baths late at night and the hot water heating doesn't come on early enough, low temp water in the morning would be the likely outcome.

Phil

[Grant]

The timer is set at the correct time and no-one has a bath late at night. What seems to be happening is that on the mornings when the water isn't as hot as usual, the boiler doesn't come for as long.

[Grant]

Set Square wrote: >

Thank you very much for your help. I will have a look tonight.

Cheers, Grant

[Grant]

Would this not mean that the radiators would get warm when the HW was on? We don't have the CH turned on in the mornings at the moment and the radiators are stone cold even on the days that the HW is not as warm as it should be.

Cheers, Grant

[Set Square]

Yes it would - so it's unlikely to be that then. [I had assumed that the heating was on as well].

In that case, it sounds more like the cylinder thermostat telling porkies - and turning the boiler and pump off before the water is hot. Check the stat setting, and check whether it clicks on and off convincingly when you turn it through the set point.

[Grant]

I don't know if this is connected or not, but whenever the HW is on but the CH is not, there are noises of water going round the radiators (presumably it is water being pumped round the system). The rads do not get hot, however. Is this normal i.e. the pump is pumping water round the rads and to the HW cylinder)?

Cheers, Grant

[Set Square]

It's certainly not normal! In HW-only mode, no water should be moving in the CH circuit. Any water which *is* moving should be hot - so if this flows through the radiators, *they* will get hot! I've no idea what's going on.