Boiler problem - hot water, cold radiators

[Dan the man]

Hi all,

We moved into our new house a few months ago, which has a Worcester

24i combi boiler. At first we had no need of the central heating (ut being a hot summer and all), but noticed that sometimes we could run the hot taps for ages (with the boiler firing up) and getting no hot water out. What we had to do was run the tap, turn it off for a few seconds, then turn it back on and the hot water would finally emerge. That wasn't too bad, as we knew that we just had to turn the taps on then off then on again.

Once the weather turned, the central heating kicked in and since then we've not had the problem with the taps - hot water comes out first time as it should.

This morning though, we woke up to find the house freezing - the central heating is on a timer, and should have kicked in about an hour before we got up. Although the boiler was fired up, the radiators were stone cold. Checked the thermostat, no problem. Anyhow, once the hot taps had been turned on so I could have a wash (hot water came out of there straight away), the radiators began to warm up, as if the act of turning the hot tap on had sparked them into action.

Knowing nothing about boilers, I hope the above information is enough for someone more knowledgeable than me to figure it out!

Something else, which is more annoying than anything else, is that when the central heating is on, the boiler will repeatedly fire up than switch off immediately, about 10-15 times before finally firing up and staying on for a while. Is this normal? I only ask as the bathroom is right next to where I work, and the noise of the boiler clicking on and off every few seconds is quite distracting!

Hope someone can make something of all this!

Cheers.

[Andy Hall]

Mr. Jones....... it's yer pump. (probably).

.andy

To email, substitute .nospam with .gl

[Christian McArdle]

Could be your diverter valve.

Christian.

[Roger Mills]

That sounds likely - or even the electronics which control the diverter valve. It sounds as if running the hot taps is resetting something which then enables the diverter valve to work.

I don't profess to know much about combis but, from my limited understanding of how they work, I would look at the control board.

Roger

[David W.E. Roberts]

Taps:

------

Sounds (from a logical view, not an expert on Combi boilers) that whatever detects that water is flowing and therefore needs heating (pressure valve?) is sticking a bit.

Open tap - no action. Open tap, close (pressure raised above norm briefly) open again (larger pressure drop) and the bolier kicks in. Effectively you are 'kicking' the pressure sensor. [Could low mains pressure make this happen also?? i.e. not enough difference between taps closed and open to trigger the pressure sensor.]

Once the boiler is going, presumably (?) it is turned off once max temperature is reached, so hot water continues to flow.

So your problem is getting the boiler to turn on not turn off.

This is supported by the fact that once the boiler is running (for the central heating) you get hot water straight away. [Although presumably this would work even if the pressure sensor was totally non-functional?]

Central Heating:

----------------

O.K. at first, but now whatever senses that the water is under temperature in the central heating circuit (or just the boiler) is not functioning (boiler thermostat?). So although water is being pumped round the boiler is not kicking in because it cannot detect that the water temperature is low (switch on).

However when you start the boiler (hot water tap pressure switch) the boiler starts, and then heats the water in the radiator circuit also. This suggests that the pump is running but the 'on' thermostat is not working.

One thing is not clear from your account.

Does the central heating only work whilst the hot tap is on? If so, the thermostat in the central heating circuit is completely thrashed.

Does the central heating warm up fully once a hot tap has been run for a little? If so it is only the 'on' action of the thermostat which is not working. [And you are going to spend a lot of time turning hot taps on for a bit to keep the house warm]

As I stated at the start, this is a (hopefully) logical analysis of the symptoms - I don't know the bits of a Combi but I am assuming:

Hot water boiler on - pressure sensor Hot water boiler off - h/w thermostat CH boiler on - c/h thermostat CH boiler off - c/h thermostat

This assumes that the valves and pump are working correctly and the timer/programmer is supplying the correct voltages.

Reading through this there are inconsistencies (you talk about the boiler 'cycling' so at some stage the 'on' and 'off' functions of the thermostat are working) but hey - logic is at best a weak and damaged tool :-)

There are also more complex interactions e.g. the hot water flow to the taps is getting too hot (so turn the boiler off) but the CH water is cool (so turn the boiler on). I presume the HW would over-ride the CH in the interest of safety but this shows that a simple analysis could be a load of tosh :-)) Also that you could just have a thrashed logic circuit in the controller.

Summary:

Sound like you have more than one problem You may have problems with your pressure sensor and your boiler thermostat. Or something else entirely.

Cheers Dave R

P.S. we seem to have a rash of 'my combi system doesn't work after the summer layoff' threads at the moment. So:

(1) As I was advised with car aircon over winter "just because you don't need it don't ignore it; switch it on at least once a month to keep it happy" so I would suggest that the CH on combi systems should perhaps be turned on at least once a month over the summer just to check it is still working and exercise the controls. At least you will know before winter if you have problems.

(2) My old conventional boiler is still running well, and we have been in the house nearly 20 years. Lord only knows how old it is, but it passed the last Corgi inspection with flying colours. It is less efficient than a modern combi but all the bits are obvious and easy to replace. Projected savings with a new combi are all very well, but if bits keep dropping off then the savings may not materialise. My mum-in-law is on her second Combi in 10 years (mind you the first one was cheap crap). I am drawn to a comparison with cars - my old Moggie Minor was slow and inefficient, but I could fix everything on it. My more recent Volvo Turbo Estate (now quite elderly) has so much electronic gadgetry under the bonnet and fancy doodads and chips and analysis sockets that it frightens me every time I open the bonnet. Faster, more powerful, etc. but a bugger if it goes wrong. So is simplicity best at times?

[Roger Mills]

thermostat.

An interesting analysis - but it doesn't quite take account of the fact that a combi boiler EITHER heats the hot water OR the central heating - but not both at the same time. It achieves this by means of an internal diverter valve which directs the heated water either through its internal heat exchanger (for hot water) or through the external circuit (for central heating).

The symptoms described suggest to me that the diverter valve is not working properly - either as a result of a problem with the valve itself or (perhaps more likely) as a result of a problem with the logic and sensors which tell the valve what to do.

Roger

[David W.E. Roberts]

Aha! As I said, I don't know much about Combis. I was assuming that it was like conventional boilers which can support multiple tappings and so could do both CH and H/W (via heat exchanger) at the same time.

This leads me on to another thought - if the combi can only do hot water or CH does this mean that the house cools down whilst the distaff side are spending an hour in the shower(s) or does the diverter flip between the heat exchanger and the CH circuit all the time, allowing both to appear to be working simultaneously?

[Roger Mills]

As far as I know, it can't timeshare - it's one or the other.

It relies on the assumption that continuous flowing hot water won't be required for very long at a time - so that the radiators won't have time to cool significantly.

Those whose water usage pattern is not like this would do well *not* to have a combi!

Roger

[Christian McArdle]

Remember that the combi is sufficiently overpowered to get the radiators hot very quickly when the hot water is not being supplied. Presumably the serial shower takers will have some sort of three minute changeover between showers. This would help keep the radiators hot in between.

Christian.

[David W.E. Roberts]

Aha - you forget the ubiquitous en-suite!