Any plumbers on here?

[GAZ W]

are there any plumbers on here, I was just wondering if you could help?

It is a problem i am having with the Boiler , Baxi 105(combi)

When i am running hot water for a bath after about 30 seconds the water starts to run cold for about 20 seconds then warms up again , its as though the boiler keeps cutting off and letting the water go cold .

It seems ok when you are having a shower and the central heating works (i did notice theat the little LED above the flame symbal took a while to come on when i first started the central heating)

thanks for any help

[RStu]

Its probably the plate heat exchanger starting to scale up. If the temperature neons on the front of boiler go to max, but the water temperature still isn't as hot as it used to be, then go cold and then hot, more than likely it is the heat exchanger. Would need flushing with a de scaling fluid and pump

[tony orrell]

are there any plumbers on here, I was just wondering if you could help?

It is a problem i am having with the Boiler , Baxi 105(combi)

When i am running hot water for a bath after about 30 seconds the water starts to run cold for about 20 seconds then warms up again , its as though the boiler keeps cutting off and letting the water go cold .

It seems ok when you are having a shower and the central heating works (i did notice theat the little LED above the flame symbal took a while to come on when i first started the central heating)

thanks for any help

Does the same thing happen when you use one of the sinks in the house, Or is it just the Bath?

[GAZ W]

Does the same thing happen when you use one of the sinks in the house, Or is it just the Bath?

Yes same thing happens with any sink , just not the shower

And central heating is fine

Temp neons are going to max too , then water going cold, then back to warm.

[GAZ W]

Its probably the plate heat exchanger starting to scale up. If the temperature neons on the front of boiler go to max, but the water temperature still isn't as hot as it used to be, then go cold and then hot, more than likely it is the heat exchanger. Would need flushing with a de scaling fluid and pump

How would this be done?

[tony orrell]

Just try to regulate the tap first before you call anyone in. A combi boiler on the domestic water side works like a electric shower, if you turn a hot tap on asking for full demand in a lot of cases the boiler cant heat it it fast enough. So just try turning the hot tap on 50% and see what happens. Also with the weather we are having what does'nt help is the water is a lot colder as it comes into your property.

[RStu]

2 ways really, either the boiler is stripped down and the heat exchanger removed, it can then be taken to a local plumbing shop that will attach a pump, to send descaling fluid back and forth, or a hire a descaling pump which you have to then attach to the mains cold in and hot out side of the boiler, (after its been shut down, drained, gas off) which will then pump the solution around, this method is better as it cleans out the rest of the boiler water ways, diversion valve, flow switch etc.
If you live in a hard water area I would think this is the problem,

[DazRS2K]

Just try to regulate the tap first before you call anyone in. A combi boiler on the domestic water side works like a electric shower, if you turn a hot tap on asking for full demand in a lot of cases the boiler cant heat it it fast enough. So just try turning the hot tap on 50% and see what happens. Also with the weather we are having what does'nt help is the water is a lot colder as it comes into your property.

This is what i have to do Gaz, try this first!!

[topaz]

gaz, your only little, 30 seconds of hot water is more than enough for a bath

[tony orrell]

Yes same thing happens with any sink , just not the shower

And central heating is fine

Temp neons are going to max too , then water going cold, then back to warm.

Was the combi fitted to a exsisting system, or was it a complete new heating system when fitted?

[mrwatt]

I have had a similar problem with my combi boiler, turned out to be the hot water sensor. it was located on the hot water outlet at the bottom of the boiler. simple fix if you are technically competent. I work with gas and electronics as a job.
If your not sure get a heating engineer in.

[GAZ W]

Was the combi fitted to a exsisting system, or was it a complete new heating system when fitted?

Existing system , boiler has been in around 3 years

Also been told to change thermistor(s) first to see if this cures it as this is more DIY than flushing a exchanger

[grum]

pmsl at Topaz

[graham John]

think andyC should start a poll to see what is the best solution

cheeRS

[tony orrell]

Existing system , boiler has been in around 3 years

Also been told to change thermistor(s) first to see if this cures it as this is more DIY than flushing a exchanger

On your existing system you will find that most of your hot water pipework will be 22mm and your cold water pipework will be 15mm. When you fit a combi your hot water supply comes straight from the incoming water main so when you turn the hot water on full demand your hot water pipes are holding 50% more water. So in effect you are asking the boiler to work its nuts off. This is a common problem where combi boilers are fitted to existing heating systems.