Pls Help - seriously confused re central heating/water setup

Postby NikkiD » Mon Nov 03, 2008 2:11 pm

Hi all

Am desperate for some expertise at the moment before I yet again embark on spending more pennies on plumbers. Sorry if this seems a bit long, will try and keep as brief as possible.

We moved into our house a year ago and have been baffled by the heating system ever since!

We have a Worcester Bosch Combi boiler, a danfoss programmer, hot water cylinder with a thermostat attached stored in one of our bedrooms, attached to which is a honeywell motorised mid-position valve. Also, we have no room thermostat, just trv's on all radiators.

The problem we have is that in order for us to have any heating, we have to select hot water on the programmer. The radiators seem to heat up fine, but some then cool down completely but the boiler continues to fire on and off every 10 mins until the programmer goes off.

If I move the adjustor on the 3 port valve from auto to override and hold this in place, I am able to select only heating on the programmer and the boiler fires up. However, if I select hot water on the programmer, the boiler will not fire no matter where I hold the adjustor on the 3 port valve. If I open any of the taps downstairs, the boiler fires up and I am able to get hot water on demand. However, I cannot get hot water on demand in the bathroom upstairs unless I have the hot water, and hence the heating on at the same time. Is this normal?

Is someone able to explain to me what kind of system this is as this is driving me crazy. We have had numerous plumbers out, all of which have stated something different. Some have said that this is just the way the system has been set up, others have said to flush the system (which we did to no avail) and the last engineer thought it was a problem with the 3 port valve. I thought that having a combi boiler would serve heating and hot water separately and therefore eliminated the need for a hot water cylinder, but hey, I'm no expert either? Also, is it not beneficial for us to have a room thermostat to control the overall temperature in the house?

Your advice would be greatly appreciated.
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Simply Build It

Postby htg engineer » Mon Nov 03, 2008 4:36 pm

Firstly you wont have a combi and a cylinder. Unless you have two systems in your house.

Cylinder - but boiler fires up and gives instant hot water when a tap is opened ?

All I can suggest is getting someone out to take a look.

I don't think you have a combi boiler, and I think the problem will be the actuator and three port valve.

The fact the boiler fires when the hot tap is opened may be coincidental, turn off the power supply to the boiler and try the tap - you'll probably still have warm/hot water (from the cylinder)

You either have two boilers/systems or you're confusing yourself - and me ;-) trying to describe what controls, boiler, cylinders etc etc that you have.

Try to find out the boiler make and model.

htg engineer
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Postby NikkiD » Tue Nov 04, 2008 1:39 pm

Hi htg engineer

The boiler is a Worcester Bosch 35cdi boiler. According to the boiler manual, this is a combi boiler!
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Postby NikkiD » Tue Nov 04, 2008 1:40 pm

Hi Htg engineer

The boiler is a Worcester Bosch 35cdi. According to the instructions, this states it is a combi boiler!
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Postby AdamsHeating » Wed Nov 05, 2008 4:51 pm

It sounds like a peppermint nightmare to me (mighty boosh quote, I love it!)

Has some crazy gas fitter gone mad on this one? I'm at a loss as to how a combi can be fitted into a gravity system. Follow the flow and return from the Wocester to the three way valve and cylinder, the pipes are the fatter 22mm ones, are they definitely connected? What about the DHW (direct hot water) from the Wocester? Is it running to the cylinder?

Some combis can be set up as system boilers, but to buy a 35kw boiler and stick it on a system is a joke unless you're heating 40 rads.

If it is a combi you want and you are competent, you should be able to do a bit of pipe cutting and pasting and eliminate the cylinder altogether.
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Postby NikkiD » Fri Nov 14, 2008 10:47 am

Hi AdamsHeating and thanks for your response

I think you're correct in saying that a crazy gas fitter has gone mad. We got a recommendation for a heating engineer who has come out to have a look. He thinks the previous owners have set the system up by trying to run 2 systems and failed miserably. He believes the problem to be a wiring problem which he will try to remedy first. Failing which he said he will have to follow the pipework through and may need to do some adjustments to pipes in order to the combi working as it should do. However, he thinks the wiring alone will cost around £300 which we thought a little steep - do you think this is a bit pricey?

He also suggested we think about installing a room thermostat as at the moment, we have trvs on all rads and are not convinced this is the most economical way to heat the house. We've had the system balanced, but it seems that once all radiators have heated satisfactorily, after about an hour all rads bar the living room completely cool down.
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