Combi Boilers - Help Please

ArthurLee

I had a Baxi Combi 130 HE fitted a year ago. Everything seemed OK apart from the water pressure keep going down. I need to 'top it up' every couple of months or so.

I normally keep the timer in the 'constant' position and adjust the radiator temperature via the thermostat in the sitting room but recently, even turning the thermostat to below zero, the radiators would still heat up slightly. With this heatwave, I decided to turn the timer 'off' permanently and to make sure that the central heating wouldn't come on at all, I set all the bezels on the timer inwards. I've even turned the main part of the boiler's displays to mimimum temperature and also have turned the central heating display to 'off'.

Now, if I turn on a hot tap for a bath or even to wash my hands the radiators come on and heat up pretty quickly. I've turned the thermostat to the lowest it will go.

A friend of mine said it sounds like the diverter valve is passing heat into the radiators when I turn on a hot tap instead of doing hot water only.

Does this sound right and what can I do about it? I've noticed that when I fill a bath, the water doesn't come out very hot unless I slow it down to a trickle. Is this typical of combi boilers?

Sorry this is long winded but your help is much appreciated

trafalgar_2

Yes I had the same problem a few weeks back and your diverter valve is sticking I don't know if it can be freed but I needed a new one

pvsol

I have a combi boiler and can get hot radiators but the hot water is cold, also the gauge which shows the pressure goes down very quickly and I have to add pressure every other day - can anyone help?

hrafndot

pvsol wrote:

I have a combi boiler and can get hot radiators but the hot water is cold, also the gauge which shows the pressure goes down very quickly and I have to add pressure every other day - can anyone help?

I have a vaillant combi and I have experienced the pressure problem. The gas fitter who came flushed out the expansion chamber and that solved the problem. I also had an expansion loop fitted to enable me to re-pressurise the boiler but since the cleaning out of the expansion chamber I have not had to use it.

Re hot water. I find that as my boiler is 20 years old it doesn't heat the hot water as efficiently when the heating is off. If I want a shower, I switch the heating on. I can get hot water without the heating on but its harder work. I think adjustments to flow rates will help with the "very hot water only if thin trickle" problem. Its not often that you need scalding hot water, you could sacrifice a little heat and obtain an improved hot water supply? Hope one of these suggestions works.

robowen

@ pvsol
Sounds like divertor valve problem here. If you goto any boiler spares with the make and model number of your boiler, you should be able to get the diaphram on its own for around £15-£25 or if you are rich you can get the whole divertor valve for around £80-£180.
The diaphram is like a rubber washer and pushes a pin upto a microswitch to switch on the gas for the hot water. Most are easy replaceable for a good plumber and you don't need to be corgi reg to do it.

@hrafndot
With respect,
Never heard of anyone flushing out an expansion chamber before - not sure why they would do that ????? check pressure - yes......re-pressurise - yes, not heard this repair before !! ?? don't know.

The filling loop (expansion loop??) is that what you mean ?? should have been fitted when the boiler was installed.

If you have to put the c/heating on to get hot water then the divertor valve needs looking at. Its not efficient at all to have the heating on just to get hot water.

Divertor valves are designed that when the c/heating is on and there is demand for hot water, its switches over and gives hot water at the expense of the heating.
In most combi cases you should get heating or hot water...not both at the same time. The heating always gives way to the hot water.

Combis are not great at delivering hot water at a great flow rate. Its common to slow the flow to get hot water especially on a low flow rate boiler.



rob

hrafndot

robowen wrote:

@ pvsol

@hrafndot
With respect,
Never heard of anyone flushing out an expansion chamber before - not sure why they would do that ????? check pressure - yes......re-pressurise - yes, not heard this repair before !! ?? don't know.

just quoting British Gas engineer

The filling loop (expansion loop??) is that what you mean ?? should have been fitted when the boiler was installed.

It wasn't

If you have to put the c/heating on to get hot water then the divertor valve needs looking at. Its not efficient at all to have the heating on just to get hot water.

Hot water works without heating on but not efficiently enough for a shower

Divertor valves are designed that when the c/heating is on and there is demand for hot water, its switches over and gives hot water at the expense of the heating.
In most combi cases you should get heating or hot water...not both at the same time. The heating always gives way to the hot water.

Combis are not great at delivering hot water at a great flow rate. Its common to slow the flow to get hot water especially on a low flow rate boiler.

rob

Oh dear, I've been told stories by British Gas and also got my terminology wrong. Sorry if it was misleading

At least Vaillant made a brilliant boiler for me which, despite its age, its still going strong. Thanks for your advice Rob

[Deleted User]

robowen wrote:

The diaphram is like a rubber washer and pushes a pin upto a microswitch to switch on the gas for the hot water.

Is this the same problem as I used to get for years with my multipoint?
The pushrod gets caked with limescale, and then jams in the gland where it passes out through the diaphragm housing.

Most are easy replaceable for a good plumber and you don't need to be corgi reg to do it.

Where does the law draw the line between what a non-corgi person can do, and what he can't?

robowen

jack_pott wrote:

Is this the same problem as I used to get for years with my multipoint?
The pushrod gets caked with limescale, and then jams in the gland where it passes out through the diaphragm housing.

May well be the same problem, however, up here we don't have the same problems with limescale as further south. All the ones I've done so far have been rust/old age.
The valve can be removed and cleaned with a new diaphram fitted. Silicone grease is used to lube the pushrod to prevent further rusting.

jack_pott wrote:

Where does the law draw the line between what a non-corgi person can do, and what he can't?

Gas ! put simply !
You can do the plumbing on the boiler but not the gas.

rob

Cagey

If a combi boiler is losing pressure I would say it was because there was a small water leak somewhere in the system.

robowen

Cagey wrote:

If a combi boiler is losing pressure I would say it was because there was a small water leak somewhere in the system.

True.
Or the diaphram in the expansion vessel is ruptured causing the expansion relief valve to blow off.

rob

[Deleted User]

robowen wrote:

The valve can be removed and cleaned with a new diaphram fitted. Silicone grease is used to lube the pushrod to prevent further rusting.

That's what the gas board kept doing for over 16 years. It doesn't solve the problem. I had a complete new heater on their advice, but the new one was the same from the outset. When the pin jams the gas keeps burning after you turn the tap off. After I'd had two explosions I threatened them with legal action and then they finally fitted a modification. (A ptfe coated pushrod, I think, so that the scale won't stick.) It's been OK for about 12 years now.
It's that sort of incompetence that makes me so keen to know what I'm allowed to do myself, (and so angry at the introduction of Part P for electrical work).