Radiators getting hot when the DHW is used - Baxi Duetec

[ringi]

I have a Baxi Duetec boiler in a property I rent out and can’t understand what is going on with it.

The tenants told me the radiators were getting hot when their children had a long shower.

I called out my normal gas safe person, he cleaned out the heat exchange and it all seemed to be working, he said there was some bits of rubber in the heat exchange. (I tested it before he left and could not feel the CH pipes getting hot.)

About a week later the tenants informed me that the radiators where once again getting hot when they use the DWP. (I have tested it and can confirm this.)

The heating has not been used in the mean time.

My normal gas safe person says I should get the system flushed, and then get him back to clean out the heat exchanger again. He will not take reasonability for the problem coming back and his “fix” not working.

I can’t understand how a blocked heat exchange would allow the radiators to get hot if the diverter value was working correctly.

I can get bexi to fix the boiler for a large fixed cost this will also give me 1 year of cover.

Thoughts please…..

 

[gasmanrob]

if it is the plate heat exchanger blocked then the restriction will force the water away from the plate to the heating circuit.

if the hot water is getting hot and remaining hot at a temperature rather then peaking and dropping in quick succession then i would lean toward the divertor valve.

 

[ringi]

Thanks,

The hot water is not getting as hot as it should and takes a lot longer to heat up then I expect with a combi. I don’t think it is peaking and drop.

The gas safe person says he check the diverter value is working.

Ps, what is a “restriction”, I understand how a Y plan and S plan work so was assuming that a combi was the same just with the tank replaced with a plate heat exchanger.

 

[lame plumber]

more likely the diverter valve needs servicing, get another technician in

 

[gasmanrob]

A plate heat exchanger is a series of plates that transfers heat created by the main heat exchanger to the how water. These plates are space roughly 1.6 mm apart and are divided up so 01010101010 the 0 representing heat from the boiler traveling left to right and the 1 representing cold water coming into the boiler right to left.

if a restriction appears on the 0 plates then the boiler either can't get rid of the heat quick enough and shuts the main burner down or pushes the water down the central heating circuit via the diverter.

If the engineer removed the ceramic plate from the diverter to check it there is a possibility that he may have split the cartridge as when these are re installed the water from under the cartridge needs to be drained. If it isn't then when the retaining nut is tightened the pressure created is unable to displace the water beneath the seating due to its tight seal and subsequently cracks the seating and allows water to pass to the heating.

the initial problem regarding a blocked heat exchanger is a common problem when new boilers are connected to old systems that haven't been thoroughly cleaned. Debris deposited in the system known as sludge/magnetite works it's way around the system and back to the boiler eventually into the plate heat exchanger. As already said these gaps are extremely small and unfortunately it won't take much to block them.

however cleaning the plate only removes a small amount of debris from the effected area. The dirt in the system remains and will build up again.

The he most effective way to deal with this is to have a system flush as suggested but then fit a magnetic filter (I recommend a magnaclean pro 2) to the return pipework of the boiler this should collect any future debris before it enters the boiler and attacks expensive parts.

And finally to answer your last point the diverter valve on a combi acts much like a y plan in that it will move between heating or hot water depending on the demand. But it will not supply heating and hot water at the same time.

where abouts are you perhaps a forum member is near you and could offer a second opinion/price to carry out the remedial work

 

[kris]

Im with the guys on this ringi . Theres not much chance of hex cloggin in a week (after cleaned) so can only be diverter . Espcially with him finding a piece of rubber. Your diverter does wot it says on the tin. It diverts between CH and HW. I wouldnt say hes liable though as he cleaned out hex and removed debri and u said it worked. So id get him back (or try someone else ) to diagnose fault.

 

[jjmmcc]

Have seen this my friend,

As Lame plumber suggests.

Heating working fine,
Call for hot water from kitchen tap. All OK. might be not so hot as used to.
Call for hot water to shower, shower working but not quiet as good as before ?
Some radiators now getting warm!

Could be a sticking diverter valve.

 

[kris]

If hex blocked your then your engineer could measure temps coming out of phex and diverter and identify where waters going and whats causing problem.

 

[Ermintrude]

Turn flow and return off under boiler , if hot wasser hotter bingo it's the cart. Ensure that u get a better engineer as changing the cart has to be done in a specific manner. GSR sounds a tad SLOW to me