Strange ch system

[wobblymike]

A few weeks back a family friend asked me to help her investigate why her gas consumption was high (19kwh plus annually in a normal 3 bed semi). I had a look at her set up and discovered that her combi boiler (4 years old) had not had a service since installation and her analogue stat (mounted in front hall) was faulty. I arranged for the gas safe engineer who looks after our system to service her boiler (and living room fire) and replace her thermostat with a digital one. This was done yesterday.
He completed these jobs without issue but called me to discuss what he had found,
The system comprises a combi boiler AND a hot water tank in the landing upstairs. He said that it appears that when the stat clicks on the boiler fires up and heats the water in the upstairs tank which feeds the upstairs bathroom taps as well as being pumped round the radiators. He said that he had not encountered such a set up before and was at a loss to understand why the combi was installed in such a way or how it was wired. Her ex husband dealt with the installation and she has no knowledge about it at all.
My friend has no idea at all and has no paperwork that she can find - it's a mess. Can anyone offer me any guidance on how such a set up works - do we need to get a specialist heating engineer in? is such a set up common?, I thought the whole idea of a combi is to do away with storage tanks etc. Looking for a steer before we go further, appreciate some help.

 

[Chalked]

Your plumber is very inexperienced!

It's quite a good system to have a combi and a cylinder. You get the advantages of instant, cheap hot water for your kitchen and utility. Then a good flow rate of hot water from your cylinder to feed the bathroom hot supplies.
I would try a different plumber if he has not come across this before.

 

[wobblymike]

thanks for the reply
i have today been round to our friends house and investigated further. Her boiler is an Alpha Intec 30c condensing combi boiler. I have checked and set the thermostat settings and the boiler fires up correctly whenever the thermostat calls for heat as it should. However whenever a hot tap is turned on anywhere in the house the boiler does NOT fire up. I also noted in her kitchen there is a timer device the sort that used to be used with older boiler systems or even back boilers. It has power to it but whether it is wired into the system I don't know. I checked the tank upstairs in the airing cupboard - it has an electric immersion heater available but it's switched off. The thermostat on the tank is set at 50 degrees and I can't move it at all so it obviously needs replacing but whether it is u/s it's actually working I don't know. My questions are these
1. It has to be the boiler heating the water in the tank but how?
2. Is it likely that the timer device in the kitchen is a player in this?
Appreciate any help

 

[wobblymike]

A quick PS to my message below.
I also noted this morning that the temperature of the hot water coming out of the hot tap was too hot to hold my hand under. As stated above the stat on the tap was immovable so I turned the temperature control for hot water at the boiler down to its lowest setting of 30 deg. Just now some 3 hours later I have been advised that the water temp out of the hot tap is as hot as ever. Questions above still stand hope this latest helps to paint the picture.

 

[buckley plumb]

Pictures would help sounds like a thermal store

 

[wobblymike]

ok i'll organise some pictures - can you tell me what a thermal store is

 

[doitmyself]

A few weeks back a family friend asked me to help her investigate why her gas consumption was high (19kwh plus annually in a normal 3 bed semi).

I think that might be wrong! I would love to have an annual gas consumption of 19kWh - it would cost me less than £1 !!!

 

[buckley plumb]

ok i'll organise some pictures - can you tell me what a thermal store is

a cylinder with a coil the boiler heats this and water from it is pumped around for heating and ho****er is heated by water from this passing through a heat exchanger heating the cold water

Hot Water Cylinder | McDonald Engineers

 

[wobblymike]

thanks i will check it out
thanks doitmyself the missing k makes all the difference it should read of course 19k kwh

 

[jonnyswamp]

Are you sure it's a combi boiler and not a system boiler, they can look very similar to the inexperienced
Also some system boilers (Vaillant I think) had the same facia/cover as a combi, even with a hot water temperature dial that looked like it worked, but didn't actually control anything
Post a photo of bottom of boiler

 

[wobblymike]

defiantly a condensing combi boiler alpha intec 30c will post piccies asap thanks

 

[Masood]

A quick PS to my message below.
I also noted this morning that the temperature of the hot water coming out of the hot tap was too hot to hold my hand under. As stated above the stat on the tap was immovable so I turned the temperature control for hot water at the boiler down to its lowest setting of 30 deg. Just now some 3 hours later I have been advised that the water temp out of the hot tap is as hot as ever. Questions above still stand hope this latest helps to paint the picture.

Which hot tap did you test? If it's one fed from the cylinder, turning down the hot water temp on the boiler won't have any effect. That knob is only for the boiler's hot water output.

Also, it could be a combi piped as a system boiler.

 

[wobblymike]

i tested using the hot water tap for the bath upstairs and the hot tap over the sink in the kitchen downstairs

 

[wobblymike]

can you explain what you mean by combi piped as system boiler - thanks

 

[buckley plumb]

Post some pictures. It would help otherwise we are guessing from what you describe

 

[wobblymike]

i will do soonest - my friend is away until tomorrow on business as soon as she returns I will take piccies - thanks

 

[wobblymike]

Thought I would explain eventual findings.
The system turns out as suggested above to be a combi boiler plumbed and wired as a system boiler - the hot water tank feeds all the hot water taps and the hot water temperature control on the combi boiler is redundant. The stat on the tank works it just needed freeing up - we set it to a point around 50 degrees where the hot water is hot enough but not so hot that you can't hold your hand in it as it runs. The timer is in circuit and works. After a lot of discussion and a cost/benefit analysis my friend decided to leave the system as it is. A big learning curve for me - many thanks to all of you who helped.