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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> oil combi problem? https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1135596503 Message started by markadams on Dec 26^th, 2005, 11:28am

Title: oil combi problem?
Post by markadams on Dec 26^th, 2005, 11:28am

Hi,

I have recently had a new Worcester bosch heatslave 20-25 oil combi boiler installed.

The issue I have (which I am not sure if it is normal or not due to never having a combi boiler before).

When I turn on the CH from cold the burner comes on heats the rads no problems. but after a little which the burner turns off (but the pump remains on). I thought it had reached the temp on the room stat but this is not the case and even when turned on fully the burner does not start again.

While the pump is on without the burner the rads start cooling again (the burner may stay off for several minutes before starting again).

The pump is on full (number 3). I did wonder if the boiler got to hot and tries to get rid of the excess heat but if so why do the rads cool down again.

if the room stat is set above about 20 then the room never seems to get hot enough for the stat to funtion.

As I said it is a completly new system, rads, valves, tank, boiler etc.

I have just totaled the size of all the rads and it comes to 15883 watts.

Also when yo run a bath the water goes cold after running for about a minute (the burner remains on but no hot water), if you turn the tap off for a minute then try again you can have another minutes hot water. I only have one bath room and the hot bath tap is the only water flowing.

Thanks for any help

Mark.

Title: Re: oil combi problem?
Post by thescruff on Dec 26^th, 2005, 12:37pm

Have you read the book and if not why not ::)

The heat slave holds 10 gallons of hot water at whatever temperature you set it at ideal below 60c.

The diverter valve is normally closed to the heating and is powered open when theres a demand from the boiler, room stat or other controls.

Room cold will be down to the radiator sizes and should have been calulated to suit the required temperature.

The pump should be on 3 and nothing else it also has an over-run switch to disipate excess heat.

If the facia mounted operating switch or programmer is set to off or set to heating only then only the pump will operate.

Get the installer back to check it out

psssst, if you turn the hot water stat fully anti clockwise it enables the rads to heat up faster.

Title: Re: oil combi problem?
Post by markadams on Dec 26^th, 2005, 4:55pm

Hi John,

Happy christmas, I hope you are well.

As for the heating problem, I was not saying that the rooms get cold (the rads go cold even when the room stat is still asking for heat and the heating is switched on).

As I said the burner comes on for a while the it turns off and the pump continues to pump (warm) water, even when the room stat has not reached temperature.

I may be silly but I thought that combi's heated the water on-demand so you do not run out of hot water?

Mark. :)

Title: Re: oil combi problem?
Post by thescruff on Dec 26^th, 2005, 6:12pm

wrote on Dec 26^th, 2005, 4:55pm:

And a happy new year to Mark :D :D

Mark you must understand the heatslave is technically not a combi in the true sense of the word, its a combination boiler that incorporates a store of domestic water that reheats rapidly when you draw water to supply 17ltrs/m at the taps.

All the time you are drawing water the heating will be off the same as a normal combi.

Heating works by having a demand from external controls, once satisfied the pump will disipate the excess water into the domestic store, the temperature range is 52c on to 82c off with a differencial of 5c in which case there will be some delay in the boiler firing.

Was this a diy job ;D ;D did you fit the 3 probes in the pocket on the left, and the domestic probe in the front of the tank.

is the system sealed or open vented, have you used plastic pipe.

Title: Re: oil combi problem?
Post by markadams on Dec 26^th, 2005, 8:47pm

Nice try (to wind me up I mean ;D) but no it was fitted my an oftec registered company (I follow all the Regs when possible). I plumbed all the rads (which are plumbed in a combination of 22 and 15mm copper. I had nothing to do with the boiler or bunded tank though.

Surely the water in the heat store should reheat fast enough to feed one hot tap (when the hot water setting is on!).

I still don't see why the rads cool down when the room stat is calling for heat (not reached temperature) and the CH setting is on.

Mark.

Title: Re: oil combi problem?
Post by thescruff on Dec 26^th, 2005, 9:38pm

I would be inclined to get them back to check a few things out.

Should be call for heat, pump on, diverter valve should open (you can see this) boiler on.

The boiler when it reaches temperature should shut down on the stat but the diverter should still be open check it out.

You could have a wire or link missing ???

Title: Re: oil combi problem?
Post by greg on Dec 27^th, 2005, 9:49pm

are the flow and return from the boiler excessively hot, ie the pump not turning to get the heta away from boiler.

has the boiler / pump been fully vented